atirage: Add ability to read from PCI option rom.

Usually there is not PCI option rom if the chip is built-in to the motherboard such as in the Beige G3.

devices/video/atirage.cpp

@@ -591,6 +591,15 @@ uint32_t ATIRage::read(uint32_t rgn_start, uint32_t offset, int size)
         return 0;
     }
 
+    // memory mapped expansion ROM region
+    if (rgn_start == this->exp_rom_addr) {
+        if (offset < this->exp_rom_size)
+            return read_mem(&this->exp_rom_data[offset], size);
+        LOG_F(WARNING, "%s: read  unmapped ROM region %08x.%c",
+            this->name.c_str(), offset, SIZE_ARG(size));
+        return 0;
+    }
+
     LOG_F(WARNING, "%s: read  unmapped aperture region %08x.%c",
           this->name.c_str(), offset, SIZE_ARG(size));
     return 0;