wil6210: add platform capabilities bitmap

Add get_capa callback to platform ops to allow reading the platform
capabilities.
Supported capabilities:
- Keeping 11ad connection during suspend
- T_POWER_ON 0 support
- Usage of external clock

Change-Id: I754d5b57c8346d3ba25cf88c52ce40c14ab3bc92
Signed-off-by: Maya Erez <merez@codeaurora.org>