x86, setup (2.6.30-stable) fix 80x34 and 80x60 console modes

x86, setup (2.6.30-stable) fix 80x34 and 80x60 console modes

Note: this is not in upstream since upstream is not affected due to the
      new "BIOS glovebox" subsystem.

As coded, most INT10 calls in video-vga.c allow the compiler to assume
EAX remains unchanged across them, which is not always the case.  This
triggers an optimisation issue that causes vga_set_vertical_end() to be
called with an incorrect number of scanlines.  Fix this by beefing up
the asm constraints on these calls.

Reported-by: Marc Aurele La France <tsi@xfree86.org>
Signed-off-by: Marc Aurele La France <tsi@xfree86.org>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>