scripts: update checkpatch based on current linux kernel version

This squashes and applies the Linux diffs to scripts/checkpatch.pl
between Linux commit 16fbf79b0f83bc75 ("Linux 5.6-rc7") and
9123e3a74ec7b93 ("Linux 5.9-rc1") except for commits identified below.

The last 1000 commits to Zephyr master were compared for checkpatch
output differences between the previous Zephyr version and this
version.  One new diagnostic about function declarations with an empty
parameter-list was introduced (FUNCTION_WITHOUT_ARGS).  The text of an
existing diagnostic was changed (DT_SPLIT_BINDING_PATCH).  The text of
LONG_LINE diagnostics was enhanced to provide the actual line length.

Linux commit dfa05c28ca7ffc0a ("checkpatch: remove email address
comment from email address comparisons") was removed because
differences in the scripts resulted in false signed-off-by check
diagnostics when a full name included characters not in Basic Latin,
due to changes in how the author name was extracted.  Earlier upstream
changes not integrated into Zephyr may be required.

Linux commit b95692f8b3000166 ("checkpatch: prefer fallthrough; over
fallthrough comments") was removed because Zephyr doesn't support the
upstream pseudo keyword.

Linux commit bdc48fa11e46f867 ("checkpatch/coding-style: deprecate
80-column warning") was edited to not actually change the 80-column
maximum line limit as this change has not been mooted for Zephyr.

Linux commit ced69da1db0b57bb ("checkpatch: fix CONST_STRUCT when
const_structs.checkpatch is missing") was edited to the CONST_STRUCT
file as that's not supported in Zephyr.

Signed-off-by: Peter A. Bigot <[email protected]>

Author: pabigot