asm-generic: make the set_fs implementation optional

Put all the set_fs related code under CONFIG_SET_FS so that
asm-generic/uaccess.h can be used for set_fs-less builds.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

include/asm-generic/uaccess.h

@@ -94,6 +94,7 @@ raw_copy_to_user(void __user *to, const void *from, unsigned long n)
 #define INLINE_COPY_TO_USER
 #endif /* CONFIG_UACCESS_MEMCPY */
 
+#ifdef CONFIG_SET_FS
 #define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
 
 #ifndef KERNEL_DS
@@ -116,6 +117,7 @@ static inline void set_fs(mm_segment_t fs)
 #ifndef uaccess_kernel
 #define uaccess_kernel() (get_fs().seg == KERNEL_DS.seg)
 #endif
+#endif /* CONFIG_SET_FS */
 
 #define access_ok(addr, size) __access_ok((unsigned long)(addr),(size))