pia-am335x: add 800 MHz for all boards with Rev 2.x silicon

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
pia-am335x: use external oscillator as TPS RTC clock source

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
pia-am335x-pm: disable VDIG1 on PM module

- unused

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
pia-am335x: update boot support for eEMMC and non-NAND devices

- don't try to boot from NAND if we know we don't have it on board
- improvements for eMMC: ENV in MMC bootpart still doesn't work
  -> probably ext csd configuration on the eMMC part necessary

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