eglfs: Put Linux-specific includes within Q_OS_LINUX guards.

This should fix the build on platforms like the BSDs, where linux/fb.h does
not exist.

Change-Id: Ia06403d71c3aaa0e177c85dcefa7986647777ae0
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Fix checking of category for printf-style qCDebug

Fixes an issue introduced in b8a38a6737a. We forgot
to check for category validness, and printed qCDebug(c, ""...)
unconditionally for compilers not supporting variadic
macros.

Change-Id: I779a97dacd7ea559f0d91473aad2c29e73ea2f89
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Konstantin Ritt <ritt.ks@gmail.com>