configs: rockchip: rock960: drop options for non-existent HW

The Rock960 doesn't contain SPI flash so drop related config options.
Signed-off-by: NPeter Robinson <pbrobinson@gmail.com>
Reviewed-by: NKever Yang <kever.yang@rock-chips.com>
Reviewed-by: NManivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

configs/rock960-rk3399_defconfig

@@ -21,7 +21,6 @@ CONFIG_SYS_PROMPT="rock960 => "
 CONFIG_CMD_BOOTZ=y
 CONFIG_CMD_GPT=y
 CONFIG_CMD_MMC=y
-CONFIG_CMD_SF=y
 CONFIG_CMD_USB=y
 # CONFIG_CMD_SETEXPR is not set
 CONFIG_CMD_TIME=y
@@ -35,7 +34,6 @@ CONFIG_MMC_DW=y
 CONFIG_MMC_DW_ROCKCHIP=y
 CONFIG_MMC_SDHCI=y
 CONFIG_MMC_SDHCI_ROCKCHIP=y
-CONFIG_SF_DEFAULT_SPEED=20000000
 CONFIG_PMIC_RK8XX=y
 CONFIG_REGULATOR_PWM=y
 CONFIG_REGULATOR_RK8XX=y