Add power, clock, jtag and heartbeat pins to package definitions

[robtaylor]

Extend utils.PackageDef to cover power, clock, jtag and heartbeat

[robtaylor]

Structure agreed,. Deailed implementation and test neeeded

[robtaylor]

PRs needed for chipflow-backend and cloud.

[Go1ets]

will go to the next release @Go1ets

[robtaylor]

Inlude PinSignature-> IOSignature change