arm64: enable bloating kernel with ext errors strings

Chase commit 8e8d3068dcbe ("amd64 GENERIC: enable bloating kernel with
ext errors strings") from amd64. In general we would like to keep
GENERIC kernel options in sync between the Tier-1 architectures.

PR: 289236
Reviewed by: andrew
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D52342