platform-mc: Add sensor manager

Added sensor_manager class. The sensor_manager class manages the timing
of sensor polling.

tested: Verified on ast2600 EVB which is connected to a PLDM device
over I

platform-mc: Add sensor manager

Added sensor_manager class. The sensor_manager class manages the timing
of sensor polling.

tested: Verified on ast2600 EVB which is connected to a PLDM device
over I2C. bmcweb can display the state of numeric sensor.

Signed-off-by: Gilbert Chen <gilbert.chen@arm.com>
Signed-off-by: Thu Nguyen <thu@os.amperecomputing.com>
Change-Id: I4257f823ea26d7fdb322cc82d847e94db056258c

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