UPSTREAM: firmware_loader: Refactor kill_pending_fw_fallback_reqs()

Rename 'only_kill_custom' and refactor logic related to it
to be more meaningful.

Bug: 309378049
Change-Id: I119d2f8c29b9b624e6c1d8546c1533d76a2cc51d
Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
Acked-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/1698330459-31776-1-git-send-email-quic_mojha@quicinc.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit 87ffa98eeee8d62a56afdad80ea697e7a6e5c354)
Signed-off-by: Srinivasarao Pathipati <quic_c_spathi@quicinc.com>