split definitions for exec.c and translate-all.c radix trees

The exec.c and translate-all.c radix trees are quite different, and
the exec.c one in particular is not limited to the CPU---it can be
used also by devices that do DMA, and in that case the address space
is not limited to TARGET_PHYS_ADDR_SPACE_BITS bits.

We want to make exec.c's radix trees 64-bit wide.  As a first step,
stop sharing the constants between exec.c and translate-all.c.
exec.c gets P_L2_* constants, translate-all.c gets V_L2_*, for
consistency with the existing V_L1_* symbols.  Though actually
in the softmmu case translate-all.c is also indexed by physical
addresses...

This patch has no semantic change.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
