arm: Remove empty level2 cache code

include/plat/bcm2837/plat/machine/hardware.h

src/arch/arm/machine/l2c_nop.c

src/plat/allwinnerA20/machine/hardware.c

src/plat/allwinnerA20/machine/l2cache.c

src/plat/am335x/machine/hardware.c

src/plat/am335x/machine/l2cache.c

src/plat/apq8064/config.cmake

src/plat/apq8064/machine/hardware.c

src/plat/apq8064/machine/l2cache.c

src/plat/bcm2837/config.cmake

src/plat/bcm2837/machine/l2cache.c

src/plat/exynos5/config.cmake

src/plat/exynos5/machine/hardware.c

src/plat/exynos5/machine/l2cache.c

src/plat/hikey/config.cmake

src/plat/hikey/machine/hardware.c

src/plat/imx7/config.cmake

src/plat/imx7/machine/hardware.c

src/plat/omap3/machine/hardware.c

src/plat/omap3/machine/l2cache.c