UBUNTU: SAUCE: vesafb: Set mtrr:3 (write-combining) as default

We had this setting from Oneiric to Saucy[1]. In Saucy it was part
of the combined patch to make vesafb a module, which was unnessesary
in Trusty as we moved back to built-in.
Was added back in Trusty but again lost after Vivid.

It will still be possible to disable mtrr by putting
  video=vesafb:nomtrr or video=vesafb:mtrr:<x>
on the kernel command-line but without that knowledge the default
will be noticably slower (especially on higher resolutions).

[1] https://lists.ubuntu.com/archives/kernel-team/2011-May/015600.html

BugLink: http://bugs.launchpad.net/bugs/1605662

(forward-ported from trusty by adapting file location)
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/video/fbdev/vesafb.c

@@ -51,7 +51,7 @@ static struct fb_fix_screeninfo vesafb_fix = {
 };
 
 static int   inverse    __read_mostly;
-static int   mtrr       __read_mostly;		/* disable mtrr */
+static int   mtrr       __read_mostly = 3;	/* enable mtrr write-comb. */
 static int   vram_remap;			/* Set amount of memory to be used */
 static int   vram_total;			/* Set total amount of memory */
 static int   pmi_setpal __read_mostly = 1;	/* pmi for palette changes ??? */