bootstd: android: add the bootargs env to the commandline

bootstd: android: add the bootargs env to the commandline

When previously using script based bootflows, the U-Boot
environment variable bootargs was used to customize the kernel
commandline at boot time.
In order to get the same behaviour, concatenate the bootflow
commandline with the contents the bootargs environment variable.

Signed-off-by: Nicolas Belin (TI.com) <nbelin@baylibre.com>
Signed-off-by: Guillaume La Roque (TI.com) <glaroque@baylibre.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Link: https://lore.kernel.org/r/20251024-botargsappend-v1-1-0b78f05f9132@baylibre.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>