cmd: mtdparts: add SYS_MTDPARTS_RUNTIME dependency on CONFIG_MTDIDS/MTDPARTS_DEFAULT

The two configuration CONFIG_MTDIDS_DEFAULT and CONFIG_MTDPARTS_DEFAULT
are not needed with mtd configuration CONFIG_SYS_MTDPARTS_RUNTIME which
allows the MTDIDS and MTDPARTS to be configured at runtime.

This patch has no defconfig impacts because CONFIG_SYS_MTDPARTS_RUNTIME
is only used by two platforms (stm32mp and igep00x0) which don't define
CONFIG_MTDIDS_DEFAULT or CONFIG_MTDPARTS_DEFAULT.

This patch solves an UBI environment load issue for NAND boot for
stm32mp15 platform. In mtd_uboot.c, when GD_FLG_ENV_READY is not set,
env_get_f() return a EMPTY string, define in default_environment[]
because CONFIG_MTDIDS_DEFAULT="" and CONFIG_MTDPARTS_DEFAULT="",
but a NULL pointer is expected to allow call of board_mtdparts_default.
Without mtdparts, the env partition [CONFIG_ENV_UBI_PART="UBI"] is not
found in env/ubi.c [CONFIG_ENV_IS_IN_UBI].

It is not a problem when env becomes ready, as these empty variables are
removed form U-Boot environment in env_import() / himport_r().

Fixes: a331017c ("Complete migration of MTDPARTS_DEFAULT / MTDIDS_DEFAULT, include in environment")
Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>