[Fix] Fix underflow in OBI typedefs

[LucaRufer]

Fix underflow in OBI type definitions.

Probem Description

Many default configs and testbenches set the signal widths of unused optional signals to 0. For some simulators (like VCS), this leads to the following problem:
Because the widths are unsigned fields in the obi_optional_cfg_t/obi_cfg_t structs, the [x_WIDTH-1:0] in the type definition results in an underflow due to the unsigned 0-1 and the simulator tries to create a [2**32-1:0] sized vector.

Proposed Solution

There are multiple ways to solve this problem:

• Convert the width fields in the obi_optional_cfg_t/obi_cfg_t structs to int instead of int unsigned types, resulting in logic [-1:0] vectors when a signal is not used. However, this does not solve the problem if some of the the typedef macros are called directly and not generated from the config.
• Using logic [$signed(x_WIDTH)-1:0] to cast the width inside the typedefs, resulting in logic [-1:0] vectors when a signal is not used.
• Checking if the width is 0 and computing logic [(x_WIDTH > 0 ? x_WIDTH : 1)-1:0], resulting in logic [0:0] vectors when a signal is not used.

For this PR, the last of these solution was implemented, using new macro OBI_TYPEDEF_MIN_WIDTH.

[micprog]

LGTM 👍