powerpc/32s: Remove capability to disable KUEP at boottime

[ Upstream commit df415cd7

 ]

Disabling KUEP at boottime makes things unnecessarily complex.

Still allow disabling KUEP at build time, but when it's built-in
it is always there.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/96f583f82423a29a4205c60b9721079111b35567.1634627931.git.christophe.leroy@csgroup.eu
Stable-dep-of: f0eee815

 ("powerpc/47x: Fix 47x syscall return crash")
Signed-off-by: Sasha Levin <sashal@kernel.org>