KVM: PPC: Book3S HV: Use load/store_fp_state functions in HV guest entry/exit

This modifies kvmppc_load_fp and kvmppc_save_fp to use the generic
FP/VSX and VMX load/store functions instead of open-coding the
FP/VSX/VMX load/store instructions.  Since kvmppc_load/save_fp don't
follow C calling conventions, we make them private symbols within
book3s_hv_rmhandlers.S.

Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Alexander Graf <agraf@suse.de>