The Platform Manager consists of two sections: an analog/CPLD section and a digital/FPGA section. These two pieces should be considered separately when calculating the power consumption.
The analog/CPLD portion of the power consumption can be taken from the Platform Manager datasheet, p. 7, DC Electrical Characteristics. The normal operation power supply current is 40 mA.
The digital/FPGA section will need to be calculated using the Lattice Power Calculator software. This software can be launched from the FPGA Logic window in PAC-Designer, under the tools->Power Calculator menu item. Alternatively, the Power Calculator can be launched from Lattice Diamond FPGA software. For more details on working with the power calculator and the FPGA section of Platform Manager, see this technical note: Power Estimation and Management for MachXO Devices. This technical note covers the basics of working with the Lattice Power Calculator and can be directly applied to the Platform Manager FPGA.