OMAP: DSS2: DSI: Remove functions dsi_vc_dcs_read_1() and dsi_vc_dcs_read_2()

Remove functions dsi_vc_dcs_read_1() and dsi_vc_dcs_read_2(), these are used
when the panel is expected to return 1 and 2 bytes respecitvely. This was manily
used for debugging purposes. These functions should be implemented in the panel
driver if needed.

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