drivers: dma_mcux_edma: Simplify cache attr macros

The dependency on the chosen node for dtcm can be expressed in Kconfig
language.

Cache we care about is CPU DCACHE, not the meaningless "MCUX Cache"

The macros can be reordered to be simpler by having only one level of
conditional (no nesting) instead of three levels.

Move this code closer in the file to where this cache attribute macro is
actually going to be used (the init macro) instead of randomly splitting
up the struct definitions at the top.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>