LF-3296-1 arm64:move elfcorehdr reservation early for crash dump kernel

commit 6745315419b8aa468afab98b02677af9e3d717de from
git://source.codeaurora.org/external/qoriq/qoriq-components/linux

elfcorehdr_addr is fixed address passed to 2nd kernel which may be conflicted
with potential reserved memory in 2nd kernel,so reserve_elfcorehdr() ahead of
early_init_fdt_scan_reserved_mem() can relieve this situation.

Signed-off-by: Nikhil Gupta <nikhil.gupta@nxp.com>
Signed-off-by: Poonam Aggrwal <poonam.aggrwal@nxp.com>
Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>
Reviewed-by: Aisheng Dong <aisheng.dong@nxp.com>
Signed-off-by: Meng Li <Meng.Li@windriver.com>