EFM8BB31F64G-QFP32 is listed as supported device on this page. http://www.keil.com/c51/chips.asp
Installed uVision version 5.14.2 but it's not there when I tried to create a project.
I already tried C51 from SiLab, that doesn't has any EMF8 device supported. SILabs support the devices in Simplicity Studio that btw uses a free full Keil as compiler. download SS from SILabs and all EFM8 devices are supported