simpl156.cpp - add workram mirror for osman (needed for truck in final stage)

[ghost]

see https://twitter.com/ohfivepro/status/1655907421687099394

[happppp]

It looks like that part is the same for all games, so it would make sense others have it.
How about this?:

void simpl156_state::common_map(address_map &map)
{
map.unmap_value_high();
map(0x000000, 0x07ffff).rom(); // rom (32-bit)
map(0x200000, 0x200003).portr("IN0");
map(0x201000, 0x201fff).ram().share("systemram").mirror(0x002000); // work ram (32-bit)
}

[ghost]

I'm not opposed to you refactoring it, I just fix the bug as reported here

[happppp]

It's a minor thing, but sure