powerpc/uaccess: Also perform 64 bits copies in unsafe_copy_to_user() on ppc32

ppc32 has an efficiant 64 bits __put_user(), so also use it in
order to unroll loops more.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/ccc08a16eea682d6fa4acc957ffe34003a8f0844.1615398498.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/uaccess.h

@@ -494,9 +494,9 @@ do {									\
 	size_t _len = (l);						\
 	int _i;								\
 									\
-	for (_i = 0; _i < (_len & ~(sizeof(long) - 1)); _i += sizeof(long))		\
-		unsafe_put_user(*(long*)(_src + _i), (long __user *)(_dst + _i), e); \
-	if (IS_ENABLED(CONFIG_PPC64) && (_len & 4)) {			\
+	for (_i = 0; _i < (_len & ~(sizeof(u64) - 1)); _i += sizeof(u64))	\
+		unsafe_put_user(*(u64 *)(_src + _i), (u64 __user *)(_dst + _i), e); \
+	if (_len & 4) {							\
 		unsafe_put_user(*(u32*)(_src + _i), (u32 __user *)(_dst + _i), e); \
 		_i += 4;						\
 	}								\