[OpenRISC] sort out the flush_icache_range mess v2

[Christoph Hellwig <hch@lst.de>]

Hi all,

flush_icache_range is mostly used for kernel address, except for the following
cases:

 - the nommu brk and mmap implementations,
 - the read_code helper that is only used for binfmt_flat, binfmt_elf_fdpic,
   and binfmt_aout including the broken ia32 compat version
 - binfmt_flat itself,

none of which really are used by a typical MMU enabled kernel, as a.out can
only be build for alpha and m68k to start with.

But strangely enough commit ae92ef8a4424 ("PATCH] flush icache in correct
context") added a "set_fs(KERNEL_DS)" around the flush_icache_range call
in the module loader, because apparently m68k assumed user pointers.

This series first cleans up the cacheflush implementations, largely by
switching as much as possible to the asm-generic version after a few
preparations, then moves the misnamed current flush_icache_user_range to
a new name, to finally introduce a real flush_icache_user_range to be used
for the above use cases to flush the instruction cache for a userspace
address range.  The last patch then drops the set_fs in the module code
and moves it into the m68k implementation.

A git tree is available here:

    git://git.infradead.org/users/hch/misc.git flush_icache_range.2

Gitweb:

    http://git.infradead.org/users/hch/misc.git/shortlog/refs/heads/flush_icache_range.2

Changes since v1:
 - fix pmem.c compilation on some s390 configs
 - drop two patches picked up by the arch maintainers