Differentiate the generated UAPI and internal headers during generation such
that the UAPI headers can be installed elsewhere.

A later patch will use this to move the UAPI headers to:

	arch/x86/include/generated/uapi/asm/

to make them easier to handle.

A previous patch added a -I for this path.

Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Dave Jones <davej@redhat.com>