powerpc/process: Remove useless #ifdef CONFIG_VSX

cpu_has_feature(CPU_FTR_VSX) returns false when CONFIG_VSX is
not set.

There is no need to enclose the test in an #ifdef CONFIG_VSX.
Remove it.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/0eb61cf0dc66d781d47deb2228498cd61d03a754.1597643221.git.christophe.leroy@csgroup.eu