mm/mips: use general page fault accounting

Use the general page fault accounting by passing regs into
handle_mm_fault().  It naturally solve the issue of multiple page fault
accounting when page fault retry happened.

Fix PERF_COUNT_SW_PAGE_FAULTS perf event manually for page fault retries,
by moving it before taking mmap_sem.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Link: http://lkml.kernel.org/r/20200707225021.200906-12-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>