drivers/dma: stm32 dmamux: fix isActiveFlag/clearFlag function array len

This commit uses dt property dma-channels instead of ll defines to
make sure every soc has correct number of function pointers defined.

While commit 5f6218a tried to fix this for g0 series, this caused
regression for other series(e.g. stm32g431). Using UTIL_LISTIFY and
dt properties this should finally be fixed and reduce boilerplate code.

Signed-off-by: Thomas Stranger <thomas.stranger@outlook.com>