The Android Image contains 3 components and params

 - kernel
 - initrd
 - second stage (optional)

 - tags addr
 - bootargs

In fast boot the initrd is mandatory, in barebox we are less restrictive
use the initrd only if present

add to env params:
aimage_noverwrite_bootargs
	Disable overwrite of the bootargs with the one present in aimage

aimage_noverwrite_tags
	Disable overwrite of the tags addr with the one present in aimage

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Magnus Damm <magnus.damm@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>