target-arm: Split NO_MIGRATE into ALIAS and NO_RAW

We currently mark ARM coprocessor/system register definitions with
the flag ARM_CP_NO_MIGRATE for two different reasons:
1) register is an alias on to state that's also visible via
   some other register, and that other register is the one
   responsible for migrating the state
2) register is not actually state at all (for instance the TLB
   or cache maintenance operation "registers") and it makes no
   sense to attempt to migrate it or otherwise access the raw state

This works fine for identifying which registers should be ignored
when performing migration, but we also use the same functions for
synchronizing system register state between QEMU and the kernel
when using KVM. In this case we don't want to try to sync state
into registers in category 2, but we do want to sync into registers
in category 1, because the kernel might have picked a different
one of the aliases as its choice for which one to expose for
migration. (In particular, on 32 bit hosts the kernel will
expose the state in the AArch32 version of the register, but
TCG's convention is to mark the AArch64 version as the version
to migrate, even if the CPU being emulated happens to be 32 bit,
so almost all system registers will hit this issue now that we've
added AArch64 system emulation.)

Fix this by splitting the NO_MIGRATE flag in two (ALIAS and NO_RAW)
corresponding to the two different reasons we might not want to
migrate a register. When setting up the TCG list of registers to
migrate we honour both flags; when populating the list from KVM,
only ignore registers which are NO_RAW.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Greg Bellows <greg.bellows@linaro.org>
Message-id: 1422282372-13735-2-git-send-email-peter.maydell@linaro.org
[PMM: changed ARM_CP_NO_MIGRATE to ARM_CP_ALIAS on new SP_EL1 and
 SP_EL2 reginfo stanzas since there was a (semantic) merge conflict
 with the patchset that added those]
