OMAP: DSS2: Represent DISPC register defines with channel as parameter

On OMAP4, we have a new DISPC channel for Overlay Manager LCD2. There is a set
of regsiters for LCD2 channel similar to the existing LCD channel, like
DISPC_CONTROL2, DISPC_DIVISOR2, DISPC_CONFIG2 and so on.

Introduce new enum members for LCD2 Channel and corresponding Overlay Manager
in display.h.

Represent the following DISPC register defines with channel as a parameter
to differentiate between LCD and LCD2 registers (and also DIGIT in some cases):

DISPC_DEFAULT_COLOR, DISPC_TRANS_COLOR, DISPC_TIMING_H, DISPC_TIMING_V,
DISPC_POL_FREQ, DISPC_DIVISOR, DISPC_SIZE_LCD, DISPC_DATA_CYCLEk,
DISPC_CPR_COEF_R, DISPC_CPR_COEF_G and DISPC_CPR_COEF_B

This parametrization helps in reducing the number of register defines for DISPC.
Replace the existing reads/writes to these registers in this new way.
Also, Introduce defines for registers DISPC_CONTROL2 and DISPC_CONFIG2 which
are used exclusively for LCD2 channel.

Signed-off-by: Sumit Semwal <sumit.semwal@ti.com>
Signed-off-by: Mukund Mittal <mmittal@ti.com>
Signed-off-by: Samreen <samreen@ti.com>
Signed-off-by: Archit Taneja <archit@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@nokia.com>