KVM: PPC: Book3S HV: sparse: prototypes for functions called from assembler

A bunch of KVM functions are only called from assembler.
Give them prototypes in asm-prototypes.h
This reduces sparse warnings.

Signed-off-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>