bcm2835_property: implement framebuffer control/configuration properties

bcm2835_property: implement framebuffer control/configuration properties

The property channel driver now interfaces with the framebuffer device
to query and set framebuffer parameters. As a result of this, the "get
ARM RAM size" query now correctly returns the video RAM base address
(not total RAM size), and the ram-size property is no longer relevant
here.

Signed-off-by: Grégory ESTRADE <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Andrew Baumann <[email protected]>
Message-id: 1457467526[email protected]
[AB: cleanup/refactoring for upstream submission]
Signed-off-by: Andrew Baumann <[email protected]>
Reviewed-by: Peter Maydell <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>