ARM: OMAP2+: AM43x: Add ID for ES1.2

ES1.2 is a minor variant of ES1.1. Major changes since ES1.1 are
updating ROM for fixing the following boot modes:
- NAND boot
- UART boot
- Ethernet boot
- USB HOST/Client boot
This patch adds ID support for AM437x ES1.2 silicon.
There are no additional kernel fixes required for ES1.2 silicon.

Latest Technical Documentation can be found here:
http://www.ti.com/lsds/ti/arm/sitara_arm_cortex_a_processor/arm_cortex_a9_core/am437x_arm_cortex_a9/tech_docs.page



Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>