xglamo_hack disabled by default

[Luca Capello]

Hello,

the xf86-video-glamo driver does not play well with the xglamo_hack:

  http://docs.openmoko.org/trac/ticket/2288

AFAIK the bug above is the only place where the workaround is
officially documented, not actually easy to find.  And even if I am
not an expert, I fully agree with Timo Jyrinki's comment:

  http://thread.gmane.org/gmane.comp.hardware.smartphones.userland/1333/focus=1337

The following patch adds a config setting to control the default value
of xglamo_hack.  With it, the workaround can be unconditionally built
(but disabled) on every distribution (we must be realistic: I am not
sure the Xglamo bug will be fixed anytime soon).

This is especially true for Debian, where we have xf86-video-glamo in
main (thus in official repositories) and an unofficial Xglamo package.
While I am in the process of removing the latter from the pkg-fso
repository (dead upstream and thus no longer supported),
xf86-video-glamo has at least one annoying bug compared to Xglamo:

  http://bugs.debian.org/529078
  http://docs.openmoko.org/trac/ticket/2288

NB, the patch is untested since agricola.debian.org (the ARM machine
used by the pkg-fso team to build kernel packages) is ATM building
another kernel package version.  Nevertheless, I thought that since it
is trivial enough, it is worth to already submit it for review.

Thx, bye,
Gismo / Luca