pia-am335x: allow env in eMMC

- add board config support for environment in eMMC boot partition

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
pia-am335x-pm: add emmc-reset gpio support

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
pia-am335x: update config

- fix duplicate define
- reduce bootdelay to 1 second

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>