drivers: dma: dma_nxp_edma: support MUX register in MP space

Some EDMA versions may have the channel MUX register in the MP
region. To support this scenario, use the `EDMA_HAS_MP_MUX_FLAG`
flag to figure out which channel MUX register to use (TCD or MP).

Signed-off-by: Laurentiu Mihalcea <laurentiu.mihalcea@nxp.com>