Log: scheduler: add graph flags functions

... instead of set_bit()/clear_bit(), which improves trace messages like:

Bit 0x00000002 set by some_function:100

to:

Graph flags 0x00000002 (pe_graph_updated_then) for some_action set by some_function:100

although in most cases, it was previously using bit operators directly, so this
is adding the trace messages in those cases.