ARM: 7948/1: hw_breakpoint: Add ARMv8 support

Add the trivial support necessary to get hardware breakpoints
working for GDB on ARMv8 simulators running in AArch32 mode.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Christopher Covington <cov@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>