mock_host_controller.c: Supports read/write request/response for 16 bit wide registers only

[shivmgg]

The current implementation of the mock_host_controller supports only 16 bit wide registers.
We need to expand it to support at least 32 bit wide registers (for, OR1K) to check and validate various commands, including read/write registers supported by GDB server program.

Here's one instance:

osd-sw/tests/unit/mock_host_controller.c

Line 321 in 4f43a19

* Add a 16 bit register read access to the mock