Bluetooth: SDP: Server: Introduce private define for max services

This is mainly done to avoid VLAs for looking up the service to handle
service search requests so that we can make sure that RX stack size
is sufficient for the defined no of services.

Change-Id: Ia99072615d9094a35bd7605ed2901e8018c0ecb2
Signed-off-by: Jaganath Kanakkassery <jaganathx.kanakkassery@intel.com>