[OE-core] Adding recipe to DEPENDS only if mesa provides virtual/opengl

[Carlos Rafael Giani]

A recipe here has support for Mesa 3D GBM based EGL contexts (which is 
needed for rendering directly to KMS framebuffers). However, this also 
needs libdrm.
I'd like to detect that the provider is Mesa3D, and if so, add libdrm to 
DEPENDS.
Perhaps it is possible to detect that libgbm is available, and I can use 
that to decide whether or not I need to add libdrm to DEPENDS?