dtc: introduce label relative path references

dtc: introduce label relative path references

Since introduction of OF_UPSTREAM flag, U-Boot's dtc must be able
to compile Kernel's device tree.

Since kernel commit 7de129f5389b ("ARM: dts: stm32: stm32mp151a-prtt1l:
Fix QSPI configuration"), label relative path references has been
introduced. These label relative path references is not supported
by current U-Boot dtc version 1.5.0: (see mailing list discussion [1]).

In order to support such label relative patch references
adds following commit from upstream DTC tree:

commit 651410e54cb9 ("util: introduce xstrndup helper")
commit ec7986e682cf ("dtc: introduce label relative path references")

[1] https://lore.kernel.org/all/20250115144428.GZ3476@bill-the-cat/T/

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>