ARM: bcm2835: Add GET_THROTTLED firmware property

Recent Raspberry Pi firmware provides a mailbox property to detect
under-voltage conditions. Here is the current definition.

The u32 value returned by the firmware is divided into 2 parts:
  - lower 16-bits are the live value
  - upper 16-bits are the history or sticky value

  Bits:
  0: undervoltage
  1: arm frequency capped
  2: currently throttled
  16: undervoltage has occurred
  17: arm frequency capped has occurred
  18: throttling has occurred
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Eric Anholt <eric@anholt.net>

include/soc/bcm2835/raspberrypi-firmware.h

@@ -75,6 +75,7 @@ enum rpi_firmware_property_tag {
 	RPI_FIRMWARE_GET_EDID_BLOCK =                         0x00030020,
 	RPI_FIRMWARE_GET_CUSTOMER_OTP =                       0x00030021,
 	RPI_FIRMWARE_GET_DOMAIN_STATE =                       0x00030030,
+	RPI_FIRMWARE_GET_THROTTLED =                          0x00030046,
 	RPI_FIRMWARE_SET_CLOCK_STATE =                        0x00038001,
 	RPI_FIRMWARE_SET_CLOCK_RATE =                         0x00038002,
 	RPI_FIRMWARE_SET_VOLTAGE =                            0x00038003,