board: phytec: common: Fix phytec_get_product_name()

board: phytec: common: Fix phytec_get_product_name()

Currently, phytec_get_product_name() function only takes care of PCM
SoM type, however in case of PCL, KSM or KSP SoM type it will return
error:

  phytec_get_product_name: Invalid SOM type

Add support for other SoM types as defined in phytec_som_type_str enum
(see phytec_som_detection.h) to get rid of the error.

While at it, also simplify switch case statements by grouping them
together. This makes it more concise and readable.

Signed-off-by: Primoz Fiser <primoz.fiser@norik.com>
Reviewed-by: Daniel Schultz <d.schultz@phytec.de>