get_maintainer.pl: update from Linux kernel v5.13-rc6

get_maintainer.pl: update from Linux kernel v5.13-rc6

Update U-Boot's version of scripts/get_maintainer.pl to sync it up with the
latest changes to the Linux kernel's version of the same script.

The last sync was with Linux kernel version v4.16. The commits to the kernel's
get_maintainer.pl since then (starting with the most recent) are:

	6343f6b71f83 get_maintainer: exclude MAINTAINERS file(s) from --git-fallback
	cdfe2d220476 get_maintainer: add test for file in VCS
	e33c9fe8b80c get_maintainer: fix unexpected behavior for path/to//file (double slashes)
	0c78c0137621 get_maintainer: add email addresses from .yaml files
	0ef82fcefb99 scripts/get_maintainer.pl: deprioritize old Fixes: addresses
	ef0c08192ac0 get_maintainer: remove uses of P: for maintainer name
	2f5bd343694e scripts/get_maintainer.pl: add signatures from Fixes: <badcommit> lines in commit message
	49662503e8e4 get_maintainer: add ability to skip moderated mailing lists
	0fbd75fd7fee get_maintainer: allow option --mpath <directory> to read all files in <directory>
	5f0baf95b1ed get_maintainer.pl: add -mpath=<path or file> for MAINTAINERS file location
	31bb82c9caa9 get_maintainer: allow usage outside of kernel tree
	0455c74788fd get_maintainer: improve patch recognition
	882ea1d64eb3 scripts: use SPDX tag in get_maintainer and checkpatch

Signed-off-by: Trevor Woerner <twoerner@gmail.com>