uapi: Define GENMASK_U128

uapi: Define GENMASK_U128

This adds GENMASK_U128() and __GENMASK_U128() macros using __BITS_PER_U128
and __int128 data types. These macros will be used in providing support for
generating 128 bit masks.

The macros wouldn't work in all assembler flavors for reasons described
in the comments on top of declarations. Enforce it for more by adding
!__ASSEMBLY__ guard.

Cc: Yury Norov <[email protected]>
Cc: Rasmus Villemoes <[email protected]>
Cc: Arnd Bergmann <[email protected]>>
Cc: [email protected]
Cc: [email protected]
Reviewed-by: Arnd Bergmann <[email protected]>
Signed-off-by: Anshuman Khandual <[email protected]>
Signed-off-by: Yury Norov <[email protected]>