SMBios for iGPU-only

[Malumen]

SystemProductName and other SMBios values should be iMac20,1 for iGPU-only setups.

Also, possibly requires enable-metal value under device properties for UHD 630.

<dict>
	<key>PciRoot(0x0)/Pci(0x2,0x0)</key>
	<dict>
		<key>AAPL,ig-platform-id</key>
		<data>BwCbPg==</data>
		<key>AAPL,slot-name</key>
		<string>Internal@0,2,0</string>
		<key>device-id</key>
		<data>mz4AAA==</data>
		<key>device_type</key>
		<string>Display controller</string>
		<key>enable-hdmi-dividers-fix</key>
		<data>AQAAAA==</data>
		<key>enable-hdmi20</key>
		<data>AQAAAA==</data>
		<key>framebuffer-con0-alldata</key>
		<data>AQEJAAAIAADHAwAA</data>
		<key>framebuffer-con0-enable</key>
		<data>AQAAAA==</data>
		<key>framebuffer-patch-enable</key>
		<data>AQAAAA==</data>
		<key>framebuffer-unifiedmem</key>
		<data>AAAAgA==</data>
		<key>hda-gfx</key>
		<string>onboard-1</string>
		<key>model</key>
		<string>Intel UHD Graphics 630 (Desktop)</string>
	       **<key>enable-metal</key>**
	       **<data>AQAAAA==</data>**
	</dict>
</dict>
</plist>