scripts/dtc: Update to upstream version v1.6.0-2-g87a656ae5ff9

This adds the following commits from upstream:

87a656ae5ff9 check: Inform about missing ranges
73d6e9ecb417 libfdt: fix undefined behaviour in fdt_splice_()
2525da3dba9b Bump version to v1.6.0
62cb4ad286ff Execute tests on FreeBSD with Cirrus CI
1f9a41750883 tests: Allow running the testsuite on already installed binary / libraries
c5995ddf4c20 tests: Honour NO_YAML make variable
e4ce227e89d7 tests: Properly clean up .bak file from tests
9b75292c335c tests: Honour $(NO_PYTHON) flag from Makefile in run_tests.sh
6c253afd07d4 Encode $(NO_PYTHON) consistently with other variables
95ec8ef706bd tests: No need to explicitly pass $PYTHON from Make to run_tests.sh
2b5f62d109a2 tests: Let run_tests.sh run Python tests without Makefile assistance
76b43dcbd18a checks: Add 'dma-ranges' check
e5c92a4780c6 libfdt: Use VALID_INPUT for FDT_ERR_BADSTATE checks
e5cc26b68bc0 libfdt: Add support for disabling internal checks
28fd7590aad2 libfdt: Improve comments in some of the assumptions
fc207c32341b libfdt: Fix a few typos
0f61c72dedc4 libfdt: Allow exclusion of fdt_check_full()
f270f45fd5d2 libfdt: Add support for disabling ordering check/fixup
c18bae9a4c96 libfdt: Add support for disabling version checks
fc03c4a2e04e libfdt: Add support for disabling rollback handling
77563ae72b7c libfdt: Add support for disabling sanity checks
57bc6327b80b libfdt: Add support for disabling dtb checks
464962489dcc Add a way to control the level of checks in the code
0c5326cb2845 libfdt: De-inline fdt_header_size()
cc6a5a071504 Revert "yamltree: Ensure consistent bracketing of properties with phandles"
0e9225eb0dfe Remove redundant YYLOC global declaration
cab09eedd644 Move -DNO_VALGRIND into CPPFLAGS
0eb1cb0b531e Makefile: pass $(CFLAGS) also during dependency generation

Signed-off-by: Rob Herring <robh@kernel.org>