ARM: UniPhier: reset NAND core in SPL for non-NAND boot mode

ARM: UniPhier: reset NAND core in SPL for non-NAND boot mode

For all the UniPhier SoCs so far, the reset signal of the NAND core
is automatically deasserted after the PLL gets stabled.
(The bit 2 of SC_RSTCTRL is default to one.)

This causes a fatal problem on the NAND controller of PH1-LD4.
For that SoC, the NAND I/O pins are not set up yet at the power-on
reset except the NAND boot mode.  As a result, the NAND controller
begins automatic device scanning with wrong I/O pins and finally
hangs up.

Actually, U-Boot dies after printing "NAND:" on the console unless
the boot mode latch detected the NAND boot mode.

To work around this problem, reset the NAND core in SPL for non-NAND
boot modes.  If CONFIG_NAND_DENALI is enabled, the reset signal is
deasserted again in U-Boot proper.  At this time, I/O pins have been
correctly set up, the device scanning should succeed.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>