ARM: DRA7: Add support for manual mode configuration

In addition to the regular mux configuration, certain pins of DRA7
require to have "manual mode" also programmed, when predefined
delay characteristics cannot be used for the interface.

struct iodelay_cfg_entry is introduced for populating
manual mode IO timings.
For configuring manual mode, along with the normal pad
configuration do the following steps:
- Select MODESELECT field of each assocaited PAD.
  CTRL_CORE_PAD_XXX[8]:MODESELECT = 1(Enable MANUAL_MODE macro along with mux)
- Populate A_DELAY, G_DELAY values that are specified in DATA MANUAL.
  And pass the offset of the CFG_XXX register in iodelay_cfg_entry.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>