net: dsa: bcm_sf2: refactor LED regs access

1. Define more regs. Some switches (e.g. BCM4908) have up to 6 regs.
2. Add helper for handling non-lineral port <-> reg mappings.
3. Add support for 12 B LED reg blocks on BCM4908 (different layout)

Complete support for LEDs setup will be implemented once Linux receives
a proper design & implementation for "hardware" LEDs.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Link: https://lore.kernel.org/r/20211229171642.22942-1-zajec5@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>