Camera: Add torch brightness control keys.

1.FLASH_INFO_STRENGTH_MAXIMUM_LEVEL : Number of brightness levels.
2.FLASH_INFO_STRENGTH_DEFAULT_LEVEL : Default brightness level for device in
TORCH mode.

The API to actually control the torch strength level and tests will be
added in the next series of changes.

bug: 200174275
Change-Id: I674885a237d734a2a45f40fa0e336b07fa649859