powerpc/machdep: Remove CONFIG_PPC_HAS_FEATURE_CALLS

Last user was removed by commit 7bbd8277 ("[PATCH] ppc64: very
basic desktop g5 sound support").

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/803779fffb4ee0801746b2173d37cea3b273f821.1630667612.git.christophe.leroy@csgroup.eu