util/lint: Update license header text for SPDX headers.

util/lint: Update license header text for SPDX headers.

In preparation to update to SPDX license headers, add identifiers
for the licenses seen in the coreboot project and create a command
line parameter allowing only SPDX license identifiers to be detected.

Here are example locations of these licenses:
Apache-2.0 - src/soc/sifive
BSD-3-Clause - Throughout coreboot & libpayload source
GPL-2.0-only - Throughout coreboot source
GPL-2.0-or-later - Throughout coreboot source
GPL-3.0-only - util/amdtools
GPL-3.0-or-later - src/lib/[gcov/libgcov/gnat]
ISC - src/lib/ubsan.c, soc/qualcomm/ipq806x/include/soc/gsbi.h, others
MIT - soc/nvidia/tegra210/mipi_dsi.c, files in mainboard/cavium/
X11 - include/device/drm_dp_helper.h, drivers/aspeed/common/ast_tables.h

Signed-off-by: Martin Roth <martin@coreboot.org>
Change-Id: I07a7ca408ac8563e03e189d05ef7729dfb6fc24e
Reviewed-on: https://review.coreboot.org/c/coreboot/+/36175
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-by: Werner Zeh <werner.zeh@siemens.com>