davinci: dm646x-evm: Add support for IDE

Controls ATA_RSTn and ATA_PWD through CPLD register 0 to enable ATA. An I2C
driver is added for the same. Calls ide init if enabled in configuration.

Signed-off-by: Hemant Pedanekar <hemantp@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>