uboot-imx

Revert "boot cmds: convert to getenv_yesno() with autostart"

This reverts commit 5a442c0addc69d0c4b58e98e5aec1cf07576debb.

This commit changed the behaviour of getenv_yesno() (both the default
behaviour and the documented behaviour for abbreviated arguments)
which resulted in problems in several areas.

Signed-off-by: Wolfgang Denk <wd@denx.de>