LoongArch: Mark __xchg() and __cmpxchg() as __always_inline

Commit ac7c3e4f ("compiler: enable CONFIG_OPTIMIZE_INLINING
forcibly") allows compiler to uninline functions marked as 'inline'.
In case of __xchg()/__cmpxchg() this would cause to reference
BUILD_BUG(), which is an error case for catching bugs and will not
happen for correct code, if __xchg()/__cmpxchg() is inlined.

This bug can be produced with CONFIG_DEBUG_SECTION_MISMATCH enabled,
and the solution is similar to below commits:
46f16195 ("MIPS: include: Mark __xchg as __always_inline"),
88356d09 ("MIPS: include: Mark __cmpxchg as __always_inline").
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

arch/loongarch/include/asm/cmpxchg.h

@@ -61,8 +61,8 @@ static inline unsigned int __xchg_small(volatile void *ptr, unsigned int val,
 	return (old32 & mask) >> shift;
 }
 
-static inline unsigned long __xchg(volatile void *ptr, unsigned long x,
-				   int size)
+static __always_inline unsigned long
+__xchg(volatile void *ptr, unsigned long x, int size)
 {
 	switch (size) {
 	case 1:
@@ -159,8 +159,8 @@ static inline unsigned int __cmpxchg_small(volatile void *ptr, unsigned int old,
 	return (old32 & mask) >> shift;
 }
 
-static inline unsigned long __cmpxchg(volatile void *ptr, unsigned long old,
-				      unsigned long new, unsigned int size)
+static __always_inline unsigned long
+__cmpxchg(volatile void *ptr, unsigned long old, unsigned long new, unsigned int size)
 {
 	switch (size) {
 	case 1: