[bcm_machdep] CFE_MEMORYSIZE and cosmetic code changes

[mizhka]

Summary

I'm trying to port FreeBSD on ASUS WL500W board with BCM4704 chip. But CFE memory enumerator doesn't work, returns 0 bytes. But there is CFE environment variable with actual RAM size: CFE_MEMORYSIZE

This fix uses CFE_MEMORYSIZE if CFE memory enumerator doesn't work. Also it removes misleading outdated comment and print error code if debug is enabled.

Test Plan

Tested on ASUS WL500W, regression test on ASUS RT-N12,16,53