thread_info: Add update_thread_flag() helpers

thread_info: Add update_thread_flag() helpers

There are a number of bits of code sprinkled around the kernel to
set a thread flag if a certain condition is true, and clear it
otherwise.

To help make those call sites terser and less cumbersome, this
patch adds a new family of thread flag manipulators

	update*_thread_flag([...,] flag, cond)

which do the equivalent of:

	if (cond)
		set*_thread_flag([...,] flag);
	else
		clear*_thread_flag([...,] flag);

Signed-off-by: Dave Martin <[email protected]>
Reviewed-by: Alex Bennée <[email protected]>
Acked-by: Steven Rostedt (VMware) <[email protected]>
Acked-by: Marc Zyngier <[email protected]>
Acked-by: Catalin Marinas <[email protected]>
Acked-by: Peter Zijlstra (Intel) <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>