meson: Specify the maximum required libdrm in dri.pc
When dealing with a regression in libdrm-2.4.101, I masked the package in Gentoo. In doing so, we discovered that Mesa's dri.pc specifies a version requirement in dri.pc for >= the version of libdrm Mesa was built against, thus preventing packages from being rebuilt with the older version of libdrm installed.
Let's reduce this version requirement to the latest libdrm required by Mesa instead, since libdrm is backward compatible.