intel: Update package name and description in libdrm_intel.pc

Currently the package name and description duplicate that of the
core libdrm. Update those to reflect reality.

Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Damien Lespiau <damien.lespiau@intel.com>