fix: list MAME's hash, plugins and floppy sounds

The libretro core passes system/mame/{hash,plugins,samples} (retro_init.cpp:111-155). Software lists are required in mamemess, where softlists are on by default. The trees and the 19 floppy samples are collected from libretro/mame at the pin.

bios/Other/mame/plugins/data/data_gameinit.lua

@@ -0,0 +1,27 @@
+local dat = {}
+
+local ver, info
+local datread = require('data/load_dat')
+datread, ver = datread.open('gameinit.dat', '# .-GAMEINIT.DAT')
+
+function dat.check(set, softlist)
+	if softlist or not datread then
+		return nil
+	end
+	local status
+	status, info = pcall(datread, 'mame', 'info', set)
+	if not status or not info then
+		return nil
+	end
+	return _p('plugin-data', 'Gameinit')
+end
+
+function dat.get()
+	return info
+end
+
+function dat.ver()
+	return ver
+end
+
+return dat