hw/misc/bcm2835_property: Add missed BCM2835 properties

hw/misc/bcm2835_property: Add missed BCM2835 properties

Our model of the bcm2835 mailbox is missing a few properties
that we need for the raspi4 kernel:
 * RPI_FWREQ_GET_CLOCKS
 * RPI_FWREQ_GET_THROTTLED
 * RPI_FWREQ_VCHIQ_INIT

Add minimal implementations of them.

Signed-off-by: Sergey Kambalin <sergey.kambalin@auriga.com>
Message-id: 20240226000259.2752893-40-sergey.kambalin@auriga.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: improved commit message]
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>