Assorted fixes and improvements to libdrm

• define ETIME in libsync.h to fix build of freedreno in Mesa [1]
• disable cairo tests to avoid circular dependency when cairo uses libGL [2]
• add TESTS option to install test programs which are always built
• build libkms on all platforms, it need not be limited to x86
• cease disabling vmwgfx, which needed patching to build

PR: 219420 [2]
Reported by: strejda [1], maficccc@gmail.com [2]
Approved by: swills (mentor)
Differential Revision: https://reviews.freebsd.org/D10841