ARM: mm: Export __sync_icache_dcache() for xen-privcmd

ARM: mm: Export __sync_icache_dcache() for xen-privcmd

Forwarded: https://marc.info/?l=linux-arm-kernel&m=153134944429241

The xen-privcmd driver, which can be modular, calls set_pte_at()
which in turn may call __sync_icache_dcache().

The call to __sync_icache_dcache() may be optimised out because it is
conditional on !pte_special(), and xen-privcmd calls pte_mkspecial().
However, in a non-LPAE configuration there is no "special" bit and the
call is really unconditional.

Fixes: 3ad0876554ca ("xen/privcmd: add IOCTL_PRIVCMD_MMAP_RESOURCE")
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Gbp-Pq: Topic bugfix/arm
Gbp-Pq: Name arm-mm-export-__sync_icache_dcache-for-xen-privcmd.patch