powerpc/sstep: make emulate_vsx_load and emulate_vsx_store static

These functions are not used outside of sstep.c

Fixes: 350779a2 ("powerpc: Handle most loads and stores in instruction emulation code")
Signed-off-by: Michal Suchanek <msuchanek@suse.de>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241001130356.14664-1-msuchanek@suse.de