tests: drivers: spi: stm32h7: Run 16-bit frames tests for DMA

Run 16-bit frames tests also when DMA is enabled. In addition,
remove the extra code required for the mentioned tests in
favor of config. files, and add test cases for nocache regions
defined in devicetree.

Signed-off-by: Daniel Gaston Ochoa <dgastonochoa@gmail.com>