KVM: PPC: Book3e: Add AltiVec support

Add AltiVec support in KVM for Book3e. FPU support gracefully reuse host
infrastructure so follow the same approach for AltiVec.

Book3e specification defines shared interrupt numbers for SPE and AltiVec
units. Still SPE is present in e200/e500v2 cores while AltiVec is present in
e6500 core. So we can currently decide at compile-time which of the SPE or
AltiVec units to support exclusively by using CONFIG_SPE_POSSIBLE and
CONFIG_PPC_E500MC defines. As Alexander Graf suggested, keep SPE and AltiVec
exception handlers distinct to improve code readability.

Guests have the privilege to enable AltiVec, so we always need to support
AltiVec in KVM and implicitly in host to reflect interrupts and to save/restore
the unit context. KVM will be loaded on cores with AltiVec unit only if
CONFIG_ALTIVEC is defined. Use this define to guard KVM AltiVec logic.

Signed-off-by: Mihai Caraman <mihai.caraman@freescale.com>
Signed-off-by: Alexander Graf <agraf@suse.de>