hw/arm/boot: Allow easier swapping in of different loader code

For AArch64 we will obviously require a different set of
primary and secondary boot loader code fragments. However currently
we hardcode the offsets into the loader code where we must write
the entrypoint and other data into arm_load_kernel(). This makes it
hard to substitute a different loader fragment, so switch to a more
flexible scheme where instead of a raw array of instructions we use
an array of (instruction, fixup-type) pairs that indicate which
words need special action or data written into them.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1385645602-18662-6-git-send-email-peter.maydell@linaro.org
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>