ARM: Remove mach-bcmring

Remove mach-bcmring as this is no longer maintained or used.

Signed-off-by: Christian Daudt <csd@broadcom.com>
Reviewed-by: Jiandong Zheng <jdzheng@broadcom.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>