ARM: mach-bcm: ARCH_BCM_MOBILE: remove one level of menu from Kconfig

remove menu "Broadcom Mobile SoC Selection"
This requires:
- selecting ARCH_BCM_MOBILE based on SoC selections
- fixup bcm_defconfig and multi_v7_defconfig to work with new menu levels.

Signed-off-by: Scott Branden <sbranden@broadcom.com>
ARM: multi_v7_defconfig: Enable Broadcom Cygnus

Enable Broadcom Cynugs platform support in multi_v7_defconfig

Signed-off-by: Ray Jui <rjui@broadcom.com>