delay: Rework udelay and ndelay

udelay() as well as ndelay() are defines and no functions and are using
constants to be able to transform a sleep time into loops and to prevent
too long udelays/ndelays. There was a compiler error with non-const 8 bit
arguments which was fixed by commit a87e553f ("asm-generic: delay.h fix
udelay and ndelay for 8 bit args"). When using a function, the non-const 8
bit argument is type casted and the problem would be gone.

Transform udelay() and ndelay() into proper functions, remove the no longer
and confusing division, add defines for the magic values and add some
explanations as well.

Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Anna-Maria Behnsen <anna-maria@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Link: https://lore.kernel.org/all/20241014-devel-anna-maria-b4-timers-flseep-v3-6-dc8b907cb62f@linutronix.de