Describe the u-boot.its generation in stm32mp15xx-dhsom-u-boot.dtsi
binman {} DT node as a replacement for current CONFIG_SPL_FIT_SOURCE
use, dispose of both u-boot-dhcom.its and u-boot-dhcor.its.

Use fdt-SEQ/config-SEQ to generate a list of fdt-N fitImage images {} and
matching configuration {} node entries. The configuration node entry names
no longer encode _somrevN_boardrevN suffix, which was never really used, so
drop this functionality by default. Rework board_fit_config_name_match() to
match on the new configuration node entry names.

Users who do need the match on _somrevN_boardrevN can either replace the
fdt-SEQ/config-SEQ with fixed fdt-N/config-N nodes which each encode the
matching 'description = "NAME_somrevN_boardrevN"' to restore the old
behavior verbatim, or better use SPL DT overlays for U-Boot control DT
the same way e.g. i.MX8MP DHCOM does to support multiple SoM and board
variants.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Patrick Delaunay <patrick.delaunay@foss.st.com>