ARM: armv7: Add C wrapper for allow_unaligned()

ARM: armv7: Add C wrapper for allow_unaligned()

Rename current assembler implementation of allow_unaligned() to
v7_arch_cp15_allow_unaligned() and add it into armv7.h header,
then add C wrapper of allow_unaligned().

This fixes misbehavior when linking U-Boot on ARMv7a i.MX6Q, where the
CPU specific allow_unaligned() implementation was ignored and instead the
__weak allow_unaligned() implementation from lib/efi_loader/efi_setup.c
was used, which led to "data abort" just before booting Linux via tftp,
in efi_dp_from_file() -> path_to_uefi() -> utf16_put() .

The problem is triggerd by 63f8309e524 ("efi_loader: fix efi_dp_from_file()") .
Adding the wrapper fixes the problem.

Fixes: 28f35d9aaec ("arm: armv7: allow unaligned memory access")
Signed-off-by: Marek Vasut <marex@denx.de>