i386: kvm: set CPUID_EXT_TSC_DEADLINE_TIMER on kvm_arch_get_supported_cpuid()

This moves the CPUID_EXT_TSC_DEADLINE_TIMER CPUID flag hacking from
kvm_arch_init_vcpu() to kvm_arch_get_supported_cpuid().

Full git grep for kvm_arch_get_supported_cpuid:

   kvm.h:uint32_t kvm_arch_get_supported_cpuid(KVMState *env, uint32_t function,
   target-i386/cpu.c:        x86_cpu_def->cpuid_7_0_ebx_features = kvm_arch_get_supported_cpuid(kvm_state, 0x7, 0, R_EBX);
   target-i386/cpu.c:            *eax = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EAX);
   target-i386/cpu.c:            *ebx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EBX);
   target-i386/cpu.c:            *ecx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_ECX);
   target-i386/cpu.c:            *edx = kvm_arch_get_supported_cpuid(s, 0xA, count, R_EDX);
   target-i386/cpu.c:            *eax = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EAX);
   target-i386/cpu.c:            *ebx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EBX);
   target-i386/cpu.c:            *ecx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_ECX);
   target-i386/cpu.c:            *edx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EDX);
   target-i386/kvm.c:uint32_t kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
   target-i386/kvm.c:        cpuid_1_edx = kvm_arch_get_supported_cpuid(s, 1, 0, R_EDX);
   target-i386/kvm.c:    env->cpuid_features &= kvm_arch_get_supported_cpuid(s, 1, 0, R_EDX);
 * target-i386/kvm.c:    env->cpuid_ext_features &= kvm_arch_get_supported_cpuid(s, 1, 0, R_ECX);
   target-i386/kvm.c:    env->cpuid_ext2_features &= kvm_arch_get_supported_cpuid(s, 0x80000001,
   target-i386/kvm.c:    env->cpuid_ext3_features &= kvm_arch_get_supported_cpuid(s, 0x80000001,
   target-i386/kvm.c:    env->cpuid_svm_features  &= kvm_arch_get_supported_cpuid(s, 0x8000000A,
   target-i386/kvm.c:        kvm_arch_get_supported_cpuid(s, KVM_CPUID_FEATURES, 0, R_EAX);
   target-i386/kvm.c:            kvm_arch_get_supported_cpuid(s, 0xC0000001, 0, R_EDX);

Note that there is only one call for CPUID[1].ECX above (*), and it is
the one that gets hacked to include CPUID_EXT_TSC_DEADLINE_TIMER, so we
can simply make kvm_arch_get_supported_cpuid() set it, to let the rest
of the code know the flag can be safely set by QEMU.

One thing I was worrying about when doing this is that now
kvm_arch_get_supported_cpuid() depends on kvm_irqchip_in_kernel(). But
the 'kvm_kernel_irqchip' global variable is initialized during
kvm_init(), that is called very early, and kvm_init() is already a
requirement to run the GET_SUPPORTED_CPUID ioctl() (as kvm_init() is the
function that initializes the 'kvm_state' global variable).

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
