arch/frv/include/asm/io.h: accept const void pointers for read{b,w,l}()

arch/frv/include/asm/io.h: accept const void pointers for read{b,w,l}()

The SMD driver is reading and writing chunks of data to iomem, and
there's an __iowrite32_copy() function for the writing part, but no
__ioread32_copy() function for the reading part.  This series adds
__ioread32_copy() and uses it in two places.

This patch (of 4):

The frv port uses compiler builtins, __builtin_read*(), for the I/O read
routines.  Unfortunately, these don't accept const void pointers although
the generic ASM implementations do, so generic code passing const pointers
to these APIs cause compilers to emit warnings.  Add wrapper functions
that cast away the const to avoid the warnings.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Cc: David Howells <dhowells@redhat.com>
Cc: <zajec5@gmail.com>
Cc: Bjorn Andersson <bjorn.andersson@sonymobile.com>
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Cc: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>