debug: add early_debug functions

with the recent changes to abort and debug_ll,
we are left without functions to call for displaying messages
before C/C++ initialization. Add such functions for allowing
early messages.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
boot.S: fix overwriting of elf header address

do not store elf header address in bss before zeroing it.

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: implement bitops.h

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
aarch64: put messages and aborts on unimplemented arch-switch.hh

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>
PORTING: debugging does not work currently

Signed-off-by: Claudio Fontana <claudio.fontana@huawei.com>