soc: mimxrt798s/hifi4: Rework linker and memory defs

Rename symbols so that they reflect purpose of defined memory regions.
Point region symbols to nodes in the DT. Move bogus IDT section before
DSP's ITCM. Move common ROM and RAM sections before the heap.

The move had to be done as these sections and the heap did overlap.

Signed-off-by: Vit Stanicek <vit.stanicek@nxp.com>