of/fdt: Consolidate duplicate code into helper functions

of/fdt: Consolidate duplicate code into helper functions

[ Upstream commit 8278cb72c60399f6dc6300c409879fb4c7291513 ]

Currently, there are many pieces of nearly identical code scattered across
different places. Consolidate the duplicate code into helper functions to
improve maintainability and reduce the likelihood of errors.

Signed-off-by: Yuntao Wang <yuntao.wang@linux.dev>
Link: https://patch.msgid.link/20251115134753.179931-2-yuntao.wang@linux.dev
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Stable-dep-of: bec5f6092bc1 ("of/fdt: Fix the len check in early_init_dt_check_for_elfcorehdr()")
Signed-off-by: Sasha Levin <sashal@kernel.org>