ARM: 9104/2: Fix Keystone 2 kernel mapping regression

This fixes a Keystone 2 regression discovered as a side effect of
defining an passing the physical start/end sections of the kernel
to the MMU remapping code.

As the Keystone applies an offset to all physical addresses,
including those identified and patches by phys2virt, we fail to
account for this offset in the kernel_sec_start and kernel_sec_end
variables.

Further these offsets can extend into the 64bit range on LPAE
systems such as the Keystone 2.

Fix it like this:
- Extend kernel_sec_start and kernel_sec_end to be 64bit
- Add the offset also to kernel_sec_start and kernel_sec_end

As passing kernel_sec_start and kernel_sec_end as 64bit invariably
incurs BE8 endianness issues I have attempted to dry-code around
these.

Tested on the Vexpress QEMU model both with and without LPAE
enabled.

Fixes: 6e121df1

 ("ARM: 9090/1: Map the lowmem and kernel separately")
Reported-by: Nishanth Menon <nmenon@kernel.org>
Suggested-by: Russell King <rmk+kernel@armlinux.org.uk>
Tested-by: Grygorii Strashko <grygorii.strashko@ti.com>
Tested-by: Nishanth Menon <nmenon@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>