platform: template: Improve comments for FW_JUMP_ADDR and FW_PAYLOAD_OFFSET

Both FW_JUMP_ADDR and FW_PAYLOAD_OFFSET, should be:
1. 4MB aligned for 32bit system
2. 2MB aligned for 64bit system

Explicitly specify the above details in config.mk comments
for template platform.

Signed-off-by: Anup Patel <anup.patel@wdc.com>