ARM: OMAP2+: dma: Define dma capabilities register bitfields and use them.

The system dma module has capabiities register indicating
the support for descriptor loading, constant fill, etc.
Use this instead of OMAP revision check to identify the features
supported runtime.

This avoids patching the code for feature SOCs which has
those capabilities.

Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>