[arch-general] License for libdrm packages

[ashark]

Hello. I was repacking amdgpu-pro deb files and when I started converting 
licences, I have noticed that libdrm* packages have a MIT Licence text in 
copyright file. I decided to check if AUR/libdrm-git and Extra/libdrm uses MIT 
licence, but they don't. I contacted Lone_Wolf (maintainer of libdrm-git) and 
he said that he used a licence from Extra/libdrm.
Should not it be changed to MIT instead of custom?