xserver-xorg: ship the exa module in a separate package

xserver-xorg: ship the exa module in a separate package

EXA is used by some Xorg video drivers, it doesn't need to be shipped unless
it's being used.  Note that it's dynamically loaded so the automatic library
dependencies won't catch this, but as far as I'm aware nothing on oe-core or
meta-oe is using EXA.

(From OE-Core rev: 1a666ee1cda3c0b74daba5881fc5f62e13deec66)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>