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

Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>