ARM: arm11: Add C wrapper for allow_unaligned()

Rename current assembler implementation of allow_unaligned() to
arm11_arch_cp15_allow_unaligned() and add it into arm11.h header,
then add C wrapper of allow_unaligned().

This fixes misbehavior when linking U-Boot, 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 c7c0ca37 ("efi_loader: fix efi_dp_from_file()") .
Adding the wrapper fixes the problem.

Fixes: d47a7746 ("arm: arm11: allow unaligned memory access")
Signed-off-by: Marek Vasut <marex@denx.de>