mtd: denali: support NAND_CMD_RNDOUT command

The function nand_flash_detect_ext_param_page() requires
NAND_CMD_RNDOUT command supported.  It is necessary to detect some
types of ONFi-compliant devices.  Without it, the error message
"unsupported command received 0x5" is shown.

Let's support this command on the Denali NAND controller driver.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Chin Liang See <clsee@altera.com>