gdb kernel server: fixup Search:memory style

This is a NFC patch to move around the Search:memory implementation so
that it doesn't exceed the standard column width and doesn't take so
much vertical space in gdb_trap.

Submitted by: Daniel O'Connor <darius@dons.net.au>
Reviewed by: cem, jhb
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D12684