keystone2: k2g: add env script to load firmware initramfs as part of boot flow

keystone2: k2g: add env script to load firmware initramfs as part of boot flow

On K2G, the PCIe SerDes h/w is a re-use from other K2 devices and SerDes
driver requires a firmware image to initialize the SerDes h/w device.
This is firmware is part of the initramfs file that is loaded to memory
in u-boot and passed to kernel as in other K2 platforms. This patch
customize the u-boot env to have this done automatically when the K2G EVM
boots up. With this, a user may be able to boot the EVM with a standard
PCIe card at the x1 PCIe slot and release image and test PCIe devices
such as NIC, SATA etc.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>