powerpc/process: Remove useless #ifdef CONFIG_ALTIVEC

cpu_has_feature(CPU_FTR_ALTIVEC) returns false when CONFIG_ALTIVEC is
not set.

There is no need to enclose the test in an #ifdef CONFIG_ALTIVEC.
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/03ba6b52344ca7c336df2bc6e3d31d736c804ae2.1597643221.git.christophe.leroy@csgroup.eu