[arch-general] License for libdrm packages

[ashark at linuxcomp.ru]

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?