UAPI: Set up uapi/asm/Kbuild.asm

UAPI: Set up uapi/asm/Kbuild.asm

Set up uapi/asm/Kbuild.asm.  This requires the mandatory headers to be
dynamically detected.  The same goes for include/asm/Kbuild.asm.  The problem
is that the header files will be split or moved one at a time, but each header
file in Kbuild.asm's list applies to all arch headers of that name
simultaneously.

The dynamic detection of mandatory files can be undone later.

Signed-off-by: David Howells <[email protected]>
Acked-by: Arnd Bergmann <[email protected]>
Acked-by: Thomas Gleixner <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Dave Jones <[email protected]>