tests: drivers: dma: Refactor tests to use data relocation

Eliminates dma tests' dependency on CONFIG_NOCACHE_MEMORY=y for
configuring dma data linker sections. This allows optionally relocating
dma source and destination data to sram or other custom linker section
on boards that don't support dma access to flash.

Signed-off-by: Maureen Helm <maureen.helm@analog.com>