drivers: ddr: Add DDR2 SDRAM controller driver for Microchip PIC32.

drivers: ddr: Add DDR2 SDRAM controller driver for Microchip PIC32.

This driver initializes PIC32 DDR2 SDRAM controller and internal DDR2 Phy module.
DDR2 controller operates in half-rate mode (upto 533MHZ frequency).

Signed-off-by: Paul Thacker <[email protected]>
Signed-off-by: Purna Chandra Mandal <[email protected]>
Reviewed-by: Daniel Schwierzeck <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Reviewed-by: Simon Glass <[email protected]>