[media] smiapp: Define macros for obtaining properties of register definitions

The register address, width and flags are encoded as a 32-bit value. Add
macros for obtaining these separately. Use the macros in register access
functions.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>