When we are mapping the initial sections in head.S we
know very well where the start and end of the kernel image
in physical memory is placed. Later on it gets hard
to determine this.

Save the information into two variables named
kernel_sec_start and kernel_sec_end for convenience
for later work involving the physical start and end
of the kernel. These variables are section-aligned
corresponding to the early section mappings set up
in head.S.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>