ARM: mach-orion5x: add missing header file <linux/vga.h>

This patch fixed following building error:
--
arch/arm/mach-orion5x/pci.c: In function 'orion5x_pci_sys_setup':
arch/arm/mach-orion5x/pci.c:563:2: error: 'vga_base' undeclared (first use in this function)
arch/arm/mach-orion5x/pci.c:563:2: note: each undeclared identifier is reported only once for each function it appears in
make[1]: *** [arch/arm/mach-orion5x/pci.o] Error 1
make[1]: *** Waiting for unfinished jobs....
--

Signed-off-by: Bryan Wu <bryan.wu@canonical.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>

arch/arm/mach-orion5x/pci.c

@@ -14,6 +14,7 @@
 #include <linux/pci.h>
 #include <linux/slab.h>
 #include <linux/mbus.h>
+#include <video/vga.h>
 #include <asm/irq.h>
 #include <asm/mach/pci.h>
 #include <plat/pcie.h>