powerpc/uaccess: Merge raw_copy_to_user_allowed() into raw_copy_to_user()

Since commit 17bc4336 ("powerpc/uaccess: Implement
unsafe_copy_to_user() as a simple loop"), raw_copy_to_user_allowed()
is only used by raw_copy_to_user().

Merge raw_copy_to_user_allowed() into raw_copy_to_user().

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/3ae114740317187e12edbd5ffa9157cb8c396dea.1612879284.git.christophe.leroy@csgroup.eu