nios2: flush_tlb_page use PID based flush

flush_tlb_page is for flushing user pages, so it should not be using
flush_tlb_one (which flushes all pages).

This patch implements it with the flush_tlb_range, which is a user
flush that does the right thing.

flush_tlb_one is made static to mm/tlb.c because it's a bit confusing.
It is used in do_page_fault to flush the kernel non-linear mappings,
so that is replaced with flush_tlb_kernel_page. The end result is that
functionality is identical.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>