mips: avoid calling memcpy() from memmove() for MIPS arch

mips: avoid calling memcpy() from memmove() for MIPS arch

This is a follow up to an incorrect fix for memmove() problem in:

commit 785dee78552f9ad06819bf7eb1adc05b43110842
Author: Petar Jovanovic <petar.jovanovic@rt-rk.com>
Date:   Mon May 6 13:29:02 2019 +0000

    mips: fix memmove() call when __ARCH_HAS_BWD_MEMCPY__ is not defined

Calling memcpy from memmove should be skipped in two cases:

a) if arch's memcpy uses a backward copying (e.g. SH4)
b) if arch's memcpy is not fully safe for overlapping regions (MIPS)

Signed-off-by: Petar Jovanovic <petar.jovanovic@rt-rk.com>