MIPS: c-r4k: Fix flush_icache_range() for EVA

flush_icache_range() flushes icache lines in a protected fashion for
kernel addresses, however this isn't correct with EVA where protected
cache ops only operate on user addresses, making flush_icache_range()
ineffective.

Split the implementations of __flush_icache_user_range() from
flush_icache_range(), changing the normal flush_icache_range() to use
unprotected normal cache ops.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14156/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>