OMAP2PLUS: DSS2: Clean up omap_display_init()

Currently, omap_display_init() maintains arrays for hwmod name(oh_name) and the
correspnding platform_device name(dev_name) needed by omap_device_build().
A variable oh_count keeps a track of the number of devices to build from oh_name
based on what omap revision it is.

Clean this up by maintaining an array of omap_dss_hwmod_data struct which is
defined for each omap revision as suggested by Tomi Valkeinen. Assign the
corresponding omap_dss_hwmod_data array struct to the pointer curr_dss_hwmod in
omap_display_init().

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