ARM: 9419/1: mm: Fix kernel memory mapping for xip kernels

ARM: 9419/1: mm: Fix kernel memory mapping for xip kernels

The patchset introducing kernel_sec_start/end variables to separate the
kernel/lowmem memory mappings, broke the mapping of the kernel memory
for xipkernels.

kernel_sec_start/end variables are in RO area before the MMU is switched
on for xipkernels.
So these cannot be set early in boot in head.S. Fix this by setting these
after MMU is switched on.
xipkernels need two different mappings for kernel text (starting at
CONFIG_XIP_PHYS_ADDR) and data (starting at CONFIG_PHYS_OFFSET).
Also, move the kernel code mapping from devicemaps_init() to map_kernel().

Fixes: a91da5457085 ("ARM: 9089/1: Define kernel physical section start and end")
Signed-off-by: Harith George <harith.g@alifsemi.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>