Add support for nvidia 304.xx drivers in xserver.

Those were already in nixpkgs, but not supported in xserver. Since some time
ago the current 310.xx dropped support for some not so new cards.
Use zoneinfo from tzdata

This fixes #50
Merge pull request #57 from cpages/master

Add support for nvidia legacy 304 to xserver
Merge pull request #50 from surr/fixes/tzdata

timezone should be taken from recent tzdata rather than glibc
efi-boot-stub: enable hook for running (fixup) commands after efibootmgr run