arm: pia-am335x-em: io configuration fix

- Disable clkout2 signal which was an alternative slow clock source for
  wl18xx. It's unused
- fix pinmux signal name for gpio2_5

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for WL18xx module

- note: ti-compat-wireless is required to build a working driver

Signed-off-by: Björn Krombholz <b.krombholz@pironex.de>
arm: pia-am335x-em: add support for BT UART OE gpio

- there is a new GPIO on rev 0.02 to enable the UART level shifter
  for the bluetooth module

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