powerpc/process: Remove useless #ifdef CONFIG_SPE

cpu_has_feature(CPU_FTR_SPE) returns false when CONFIG_SPE is
not set.

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

CPU_FTR_SPE only exists on 32 bits. Define it as 0 on 64 bits.

We have a couple of places like:

 #ifdef CONFIG_SPE
	if (cpu_has_feature(CPU_FTR_SPE)) {
		do_something_that_requires_CONFIG_SPE
	} else {
		return -EINVAL;
	}
 #else
	return -EINVAL;
 #endif

Replace them by a cleaner version:

	if (cpu_has_feature(CPU_FTR_SPE)) {
 #ifdef CONFIG_SPE
		do_something_that_requires_CONFIG_SPE
 #endif
	} else {
		return -EINVAL;
	}

When CONFIG_SPE is not set, this resolves to an unconditional
return of -EINVAL

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/698df8387555765b70ea42e4a7fa48141c309c1f.1597643221.git.christophe.leroy@csgroup.eu