scripts/dtc: Update to upstream version v1.4.4

This adds the following commits from upstream:

558cd81bdd43 dtc: Bump version to v1.4.4
c17a811c62eb fdtput: Remove star from value_len documentation
194d5caaefcb fdtget: Use @return to document the return value
d922ecdd017b tests: Make realloc_fdt() really allocate *fdt
921cc17fec29 libfdt: overlay: Check the value of the right variable
9ffdf60bf463 dtc: Simplify asm_emit_string() implementation
881012e44386 libfdt: Change names of sparse helper macros
bad5b28049e5 Fix assorted sparse warnings
672ac09ea04d Clean up gcc attributes
49300f2ade6a dtc: Don't abuse struct fdt_reserve_entry

Signed-off-by: Tom Rini <trini@konsulko.com>

scripts/dtc: Update to upstream version v1.4.3

Using the update-dtc-source.sh script from Linux v4.14-rc1 import the
portions of dtc that we require. We bring in update-dtc-source.sh and
scripts/dtc/Makefile from Linux v4.14-rc1. Rework DTC_FLAGS handling to
not require a test.

Signed-off-by: Tom Rini <trini@konsulko.com>