MIPS: Fix get_user_page_fast() for mips with cache alias
get_user_pages_fast() is missing cache flushes for MIPS platforms with
cache aliases. Filesystem failures observed with DirectIO operations due
to missing flush_anon_page() that use page coloring logic to work with
cache aliases. This fix falls through to take slow_irqon path that calls
get_user_pages() that has required logic for platforms where
cpu_has_dc_aliases is true.
[ralf@linux-mips.org: Explicity include <asm/cpu-features.h>.]