rockchip: rk3328-rock64: Enable boot from SPI NOR flash

Add Kconfig options to enable support for booting from SPI NOR flash on
Pine64 Rock64.

The generated bootable u-boot-rockchip-spi.bin can be written to 0x0 of
SPI NOR flash. The FIT image is loaded from 0x60000, same as on RK35xx
boards.

  => sf probe
  SF: Detected gd25q128 with page size 256 Bytes, erase size 4 KiB, total 16 MiB

  => load mmc 1:1 10000000 u-boot-rockchip-spi.bin
  1359872 bytes read in 65 ms (20 MiB/s)

  => sf update ${fileaddr} 0 ${filesize}
  device 0 offset 0x0, size 0x14c000
  1118208 bytes written, 241664 bytes skipped in 8.516s, speed 163516 B/s

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>