firmware: Add relocatable FW_JUMP_ADDR and FW_JUMP_FDT_ADDR

If FW_PIC=y is defined, the fw_jump.bin will be broken if
FW_TEXT_START is wrong. This is not the desired behavior.

Add two new variables to identify relocatable jump address:
FW_JUMP_OFFSET and FW_JUMP_FDT_ADDR. To keep the existing
ABI, FW_JUMP_ADDR and FW_JUMP_FDT_ADDR is prefered if they
are defined.

Signed-off-by: Inochi Amaoto <inochiama@outlook.com>
Reviewed-by: Anup Patel <anup@brainfault.org>