keystone2: env: add env script for booting with an initramfs with firmware

keystone2: env: add env script for booting with an initramfs with firmware

This patch updates the env script to include a initramfs with firmware
loaded and provided to kernel through second argument of bootz command
during boot. Defined DEFAULT_FW_INITRAMFS_BOOT_ENV to have all of the
required env variables and use it in evm specific config file.

The K2 linux drivers for PCIe and NetCP (1G, 10G) requires serdes
firmwares. These requires firmware to be available early through the boot
process in some cases to satisfy firmware requests from driver. Hence use
a small initramfs to provide the same and update boot env to accommodate
this in the boot flow. This method is used when rootfs is nfs and ubifs.
This fs contains just lib/firmware folder with all required firmware.

When rootfs is on initramfs, then the filesystem has the firmware under
lib/firmware and this early initramfs is not required and is not used.

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