Enabled DAP (debug access port) by default. This enables the hw-
breakpoint framework to make use of the breakpoints and watchpoints
supported by hardware.

[    0.215805] hw-breakpoint: found 2 (+1 reserved) breakpoint and 1 watchpoint registers.
[    0.224624] hw-breakpoint: maximum watchpoint size is 4 bytes.

Without this clock, the hw-breakpoint driver claims an undefined
instruction during initialization:
[    0.227380] hw-breakpoint: Debug register access (0xee003e17) caused undefined instruction on CPU 0
[    0.227519] hw-breakpoint: CPU 0 failed to disable vector catch
Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>