i386: print all GPRs, PSL, and CR3 on double fault

Also compactify the printfs, and remove comment about 'two prints'.
Their arguments are on same page, so one fault implies another.

Reviewed by: jhb
Tested by: pho
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Differential revision: https://reviews.freebsd.org/D36302