efi/libstub: arm: implement KASLR

This wires up the new KASLR implementation for ARM to the random number
generator and memory allocation routines in the UEFI stub.

Given how the UEFI stub keeps track of the placement of the DTB and
potentially an initrd via its memory map, we can quite simply use
efi_random_alloc() to carve out a window for the kernel proper, and
inform the decompressor about this by setting the kaslr_offset variable

Since the presence of a vmalloc= command line option complicates the
calculations involved, let's just disable KASLR for now if a vmalloc=
command line argument was provided.

Cc: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
1 file changed