Refactor fvp gic code to be a generic driver

Refactor the FVP gic code in plat/fvp/fvp_gic.c to be a generic ARM
GIC driver in drivers/arm/gic/arm_gic.c. Provide the platform
specific inputs in the arm_gic_setup() function so that the driver
has no explicit dependency on platform code.

Provide weak implementations of the platform interrupt controller
API in a new file, plat/common/plat_gic.c. These simply call through
to the ARM GIC driver.

Move the only remaining FVP GIC function, fvp_gic_init() to
plat/fvp/aarch64/fvp_common.c and remove plat/fvp/fvp_gic.c

Fixes ARM-software/tf-issues#182

Change-Id: Iea82fe095fad62dd33ba9efbddd48c57717edd21
diff --git a/plat/fvp/bl32_fvp_setup.c b/plat/fvp/bl32_fvp_setup.c
index 3c09ca2..901c585 100644
--- a/plat/fvp/bl32_fvp_setup.c
+++ b/plat/fvp/bl32_fvp_setup.c
@@ -83,7 +83,7 @@
  ******************************************************************************/
 void bl32_platform_setup(void)
 {
-
+	fvp_gic_init();
 }
 
 /*******************************************************************************