arm: pia-am335x-em: add pinmux for used UARTs

- already set in u-boot, but make sure pins are defined correctly

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for S0 input

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for USB OSC inputs

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for gsm module control IOs

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for EMMC reset signal

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: fix default state of gsm module control pins

- PWRKEY and EMERG_OFF use a reverse logic

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