Bluetooth: Host: Add const prefix for UUID

Add const prefix for service uuid and char uuid.

Since Service UUID and Char UUID should not change in the service
definition, they are most reasonably defined as rodata, also for
save some ram footprint.

The field `attr->user_data` type is `void *`, as this PR change
all Service UUID to rodata, so there must add (void *) to avoid warning.

Signed-off-by: Lingao Meng <menglingao@xiaomi.com>