cgem: add support for ethernet on RP1 chip found on Raspberry Pi 5

[mmel]

Summary

Add compatible string "raspberrypi,rp1-gem" with a new hardware quirk
HWQUIRK_HWCLK to indicate that the IP block provides its own clock
management and we should not override the pclk frequency.

Do other improvement:

• Switch MAC address retrieval to the new fdt_ether_get_macaddr() helper (which respects "mac-address"/"local-mac-address" properties and falls back gracefully).
• Convert some flags to bool for clarity (neednullqs, rxhangwar, have_hwclk).
• Significantly improve clock retrieval and enabling code with better error handling and proper cleanup paths.

MFC after: 2 weeks

[emaste]

Switching to bool and cgem_get_mac rework LGTM and could be committed independently if you like. I haven't looked at the rest yet.

sys/dev/cadence/if_cgem.c

136

perhaps reorder the struct to put the bools together