rockchip: jaguar-rk3588: enable SARADC and derivatives

The SARADC is used on Jaguar for multiple things:
- channel 0 is used (at runtime) as a BIOS button,
- channel 2 is exposed on the Mezzanine connector for customer specific
  logic,
- channel 5 and 6 are used for identification,

Since the SARADC requires a vref-supply provided by the RK806 PMIC, its
support and the support for its regulators are also enabled.

The button, adc, pmic and regulator commands are also enabled for CLI
use in U-Boot for debugging and scripting purposes.

The RK806 PMIC on Jaguar being routed on the SPI bus, let's enable
Rockchip SPI controller driver.

Finally, the SARADC channel 1 on Jaguar is hardwired so will never
change in the lifetime of a unit, for that reason, disable the Rockchip
Download Mode check by setting ROCKCHIP_BOOT_MODE_REG symbol to 0.

Cc: Quentin Schulz <foss+uboot@0leil.net>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Quentin Schulz <quentin.schulz@theobroma-systems.com>