ARM: twister: add missing gpio clock init

Commit f33b9bd3 breaks boards
which do not explicitly enable the gpio clocks. This causes
the twister spl to hang, since it uses the no longer enabled
gpio 55. Add CONFIG_OMAP3_GPIO_2 to unbrick the board.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Tapani Utriainen <tapani@technexion.com>
Signed-off-by: Jeroen Hofstee <jeroen@myspectrum.nl>
Acked-by: Stefano Babic <sbabic@denx.de>