mm: page-flags-layout.h: change the KASAN_TAG_WIDTH for HW_TAGS

KASAN_TAG_WIDTH is 8 bits for both (HW_TAGS and SW_TAGS), but for HW_TAGS
the KASAN_TAG_WIDTH can be 4 bits bits because due to the design of the
MTE the memory words for storing metadata only need 4 bits. Change the
preprocessor define KASAN_TAG_WIDTH for check if SW_TAGS is define, so
KASAN_TAG_WIDTH should be 8 bits, but if HW_TAGS is define, so
KASAN_TAG_WIDTH should be 4 bits to save a few flags bits.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Guilherme Giacomo Simoes <[e-mail]>
Suggested-by: Andrey Konovalov <[e-mail]>
Reviewed-by: Andrey Konovalov <[e-mail]>
Cc: Pasha Tatashin <[e-mail]>
Cc: Suren Baghdasaryan <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>

include/linux/page-flags-layout.h

···
 #define NODE_NOT_IN_PAGE_FLAGS	1
 #endif
 
-#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
+#if defined(CONFIG_KASAN_SW_TAGS)
 #define KASAN_TAG_WIDTH 8
+#elif defined(CONFIG_KASAN_HW_TAGS)
+#define KASAN_TAG_WIDTH 4
 #else
 #define KASAN_TAG_WIDTH 0
 #endif