xserver-xorg: Add mesa-dri to depends instead of virtual/libgl

xserver-xorg: Add mesa-dri to depends instead of virtual/libgl

Fixes the compile problems e.g.

| checking for GL... yes
| checking for DRIPROTO... yes
| checking for DRI... no
| configure: error: Package requirements (glproto >= 1.4.14 dri >=
7.8.0) were not met:
|
| No package 'dri' found
|
| Consider adjusting the PKG_CONFIG_PATH environment variable if you
| installed software in a non-standard prefix.

(From OE-Core rev: 966f28c29a149dca3035e2c37ccf54ed82713bdf)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>