mbox: bcm2835: Extract properties message functions to common file.

Signed-off-by: Craig McGeachie <slapdau@yahoo.com.au>
mbox: bcm2835: Simplify cell references.

Signed-off-by: Craig McGeachie <slapdau@yahoo.com.au>
mbox: bcm2835: Change mailbox channel DTS config to sub nodes

Signed-off-by: Craig McGeachie <slapdau@yahoo.com.au>
Merge branch 'master' into topic/thermal
bcm2835: thermal: Implement probe deferral to wait for mailbox.

Signed-off-by: Craig McGeachie <slapdau@yahoo.com.au>