arch: arm64: disable hardware breakpoints

Some targets like msm8994 doesn't bootup yet with
hardware breakpoint support enabled. Disable them
until we have them booting with the support.

Change-Id: Ieb92bb51142aaf2eb4554d3b41d037c045f2d75f
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>