k2g: env: Allow use of a script and plain text env files

k2g: env: Allow use of a script and plain text env files

For development purposes, it is easier to use the env import command
and plain text or script files instead of script-images. So allow
u-boot to load env var from a text file or a script file.

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