ARM: AM33xx+: Update ioregs to pass different values

Currently same value is programmed for all ioregs. This is not
the case for all SoC's like AM4372. So adding a structure for ioregs
and updating in all board files. And also return from config_cmd_ctrl()
and config_ddr_data() functions if data is not passed.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
[trini: Fixup dxr2, cm_t335, adapt pcm051 rev3]
Signed-off-by: Tom Rini <trini@ti.com>