[U-Boot] Recent changes break our update scripts, because of getenv_yesno()

[Reinhard Meyer]

Dear Wolfgang Denk,
> Dear Reinhard Meyer,
>
> In message<4D1DB35A.3090105 at emk-elektronik.de>  you wrote:
>>
>> OK, digging deeper, the culprit actually is:
>>
>> 2010-11-28
>> 	Mike Frysinger
>> 	boot cmds: convert to getenv_yesno() with autostart
>
> There has been agreement to revert that commit.
OK, I must have missed that agreement ;)

What about adding a second parameter to getenv_yesno(), that
gives the default value when the env var does not exist?

And maybe move that function into env related source?

Best Regards,
Reinhard