ARM: hisi: Fix platmcpm compilation when ARMv6 is selected

When compiling with "ARCH=arm" and "allmodconfig",
with commit: 9cdc9991 [2/7] ARM: hisi: enable MCPM implementation
we will get:

   /tmp/cc6DjYjT.s: Assembler messages:
   /tmp/cc6DjYjT.s:63: Error: selected processor does not support ARM mode `ubfx r1,r0,#8,#8'
   /tmp/cc6DjYjT.s:761: Error: selected processor does not support ARM mode `isb '
   /tmp/cc6DjYjT.s:762: Error: selected processor does not support ARM mode `dsb '
   /tmp/cc6DjYjT.s:769: Error: selected processor does not support ARM mode `isb '
   /tmp/cc6DjYjT.s:775: Error: selected processor does not support ARM mode `isb '
   /tmp/cc6DjYjT.s:776: Error: selected processor does not support ARM mode `dsb '
   /tmp/cc6DjYjT.s:795: Error: selected processor does not support ARM mode `isb '
   /tmp/cc6DjYjT.s:801: Error: selected processor does not support ARM mode `isb '
   /tmp/cc6DjYjT.s:802: Error: selected processor does not support ARM mode `dsb '

Fix platmcpm compilation when ARMv6 is selected.

Signed-off-by: Wei Xu <xuwei5@hisilicon.com>
Signed-off-by: Olof Johansson <olof@lixom.net>