Simplify the payload power state machine, add proper support to all 'FRU Control Commands'

[augustofg]

The current vTaskPayload task is hard to understand and doesn't implement all FRU Control Options in a usable way. We should decide what each command will do, trying to conform with the AdvancedTCA standard.

The FRU Control Command has the following options:

0x00 Cold Reset
0x01 Warm Reset
0x02 Graceful Reboot
0x03 Issue a Diagnostic Interrupt

Please check the PICMG 3.0 R3.0 AdvancedTCA Base Specification pages 3-60, 3-61 and 3-62.

[augustofg]

This can be done at the same time as #130

[augustofg]

May be it would be better to also check PICMG Advanced Mezzanine Card AMC.0 Specification R2.0, pages 3-75 and 3-76.