sched: avoid using ilog2() in sched.h

<linux/sched.h> indirectly via cpumask.h path includes the ilog2.h header
to calculate ilog2(TASK_REPORT_MAX).  The following patches drops sched.h
dependency on cpumask.h, and to have a successful build, the header has to
be included explicitly.

sched.h is a frequently included header, and it's better to keep the
dependency list as small as possible.  So, instead of including ilog2.h
for a single BUILD_BUG_ON() check, the same check may be implemented by
taking exponent of the other part of equation.

Link: https://lkml.kernel.org/r/20240528005648.182376-3-yury.norov@gmail.com
Signed-off-by: Yury Norov <yury.norov@gmail.com>
Cc: Amit Daniel Kachhap <amit.kachhap@gmail.com>
Cc: Anna-Maria Behnsen <anna-maria@linutronix.de>
Cc: Christoph Lameter <cl@linux.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Dennis Zhou <dennis@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ulf Hansson <ulf.hansson@linaro.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Yury Norov <yury.norov@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

include/linux/sched.h

@@ -1604,7 +1604,7 @@ static inline char task_index_to_char(unsigned int state)
 {
 	static const char state_char[] = "RSDTtXZPI";
 
-	BUILD_BUG_ON(1 + ilog2(TASK_REPORT_MAX) != sizeof(state_char) - 1);
+	BUILD_BUG_ON(TASK_REPORT_MAX * 2 != 1 << (sizeof(state_char) - 1));
 
 	return state_char[state];
 }