ARM: dts: Add restart-reason and pil sub nodes in imem

The restart reason imem cookie is required for reboot
bootloader command to work. The pil imem cookie is
required to save the load addresses for various sub-systems.

Change-Id: Ifb6fda12a2763b79987c70b9308ed9f335ebcfd3
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>