mfd: bcm2835-pm: Use 'reg-names' to get resources

If available in firmware, find resources by their 'reg-names' position
instead of relying on hardcoded offsets. Care is taken to support old
firmware nonetheless.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20220625113619.15944-7-stefan.wahren@i2se.com