da850evm : enable NAND even when not in NAND boot mode

There is currently no NAND pinmux enabled by the da850evm board setup code.
This is fine when booting from NAND since the early boot code (UBL) will setup
the pinmux; however, when the boot mode is any other setting NAND is unusable
when enabled in the config.

This patch adds a pinmux list for NAND and enables it when NAND is enabled in
the config. Tested by booting from SPI on the da850evm and verifying NAND
was usable.

Signed-off-by: Ben Gardiner <bengardiner@nanometrics.ca>
CC: Nick Thompson <nick.thompson@ge.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>