scripts/gdb: handle split debug for vmlinux

scripts/gdb: handle split debug for vmlinux

This is related to two previous changes.  Commit 6b77697dca0a
("scripts/gdb: find vmlinux where it was before") and commit a5e8c18f9bb4
("scripts/gdb: handle split debug").

Although Chrome OS has been using the debug suffix for modules for a
while, it has just recently started using it for vmlinux as well.  That
means we've now got to improve the detection of "vmlinux" to also handle
that it might end with ".debug".

Link: https://lkml.kernel.org/r/20211028151120.v2.1.Ie6bd5a232f770acd8c9ffae487a02170bad3e963@changeid
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Cc: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Kieran Bingham <kbingham@kernel.org>
Cc: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>