[MIPS] Print Config7 on boot for several MIPS architectures

Config7 contains useful fields, for instance, field AR indicating that the D-cache is configured to avoid cache aliases. This patch brings printing of config7 for MIPS 24K, 74K, 1004K.

Reviewed by: adrian
Approved by: adrian (mentor)
Differential Revision: https://reviews.freebsd.org/D8514