arm: support zImage format kernels for dom0

arm: support zImage format kernels for dom0

Allow a zImage format kernel to be used for dom0.  zImages are (by
default) hardcoded with the RAM location so adjust the RAM in the
memory map to match the physical memory map (0x80000000).

Vmlinux ELF images are loaded using a hack to locate the RAM so the
IPA is the same as the kernel's VA so the elf loader does the right
thing.  If an ELF image is loaded the RAM will be located at
0xC0000000 (as before).

Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Committed-by: Ian Campbell <ian.campbell@citrix.com>