boards: shields: dvp_fpc24_mt9m114: search shield in lowercase

The script zephyr/scripts/kconfig/kconfigfunctions.py used by
Kconfig's "shields_list_contains" searches shield names in lower-case,
like they are passed through the SHIELD in CMake, --shield argument
in west. Make the mt9m114 shield upper-case. This has no effect currently
as this Kconfig entry is not used anywhere in Zephyr.

Signed-off-by: Josuah Demangeon <me@josuah.net>