microblaze: remove asm-generic wrapper headers

Some of microblaze's asm and uapi header are merely including their
asm-generic counterpart. Thus, the arch specific headers can be removed
and the asm-generic header can be used directly via generic-y.

The headers removed from uapi don't need to be added to generic-y in the
uapi Kbuild in order to get exported, as they are already listed in
mandatory-y.

Also order the generic-y list alphabetically.

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>