ARM: hw_breakpoint: Enable debug powerdown only if system supports 'has_ossr'

ARM: hw_breakpoint: Enable debug powerdown only if system supports 'has_ossr'

Commit {9a6eb31 ARM: hw_breakpoint: Debug powerdown support for self-hosted
debug} introduces debug powerdown support for self-hosted debug.
While merging the patch 'has_ossr' check was removed which
was needed for hardwares which doesn't support self-hosted debug.
Pandaboard (A9) is one such hardware and Dietmar's orginial
patch did mention this issue.
Without that check on Panda with CPUIDLE enabled, a flood of
below messages thrown.

[ 3.597930] hw-breakpoint: CPU 0 failed to disable vector catch
[ 3.597991] hw-breakpoint: CPU 1 failed to disable vector catch

So restore that check back to avoid the mentioned issue.

Cc: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Will Deacon <will.deacon@arm.com>
Reported-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>