OMAPDSS: encoder-tpd12s015: Fix race issue with LS_OE

OMAPDSS: encoder-tpd12s015: Fix race issue with LS_OE

A race issue has been observed with the encoder-tpd12s015 driver, which
leads to errors when trying to read EDID. This has only now been
observed, as OMAP4 and OMAP5 boards used SoC's GPIOs for LS_OE GPIO. On
dra7-evm boards, the LS_OE is behind a i2c controlled GPIO expander,
which increases the time to set the LS_OE.

This patch simplifies the handling of the LS_OE gpio in the driver by
removing the interrupt handling totally. The only time we actually need
to enable LS_OE is when we are reading the EDID, and thus we can just
set and clear the LS_OE gpio inside the read_edid() function.

This also has the additional benefit of very slightly decreasing the
power consumption.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>