legacy rtc: remove needless/confusing HPET_RTC_IRQ option

HPET_RTC_IRQ is no longer needed; HPET_EMULATE_RTC suffices and is more
correct.  (http://bugzilla.kernel.org/show_bug.cgi?id=11111

)

Note that when using the legacy RTC driver, platforms don't really do a
dynamic switch between HPET and non-HPET modes based on whether HPET
hardware actually exists ...  only rtc-cmos (using the new RTC framework)
currently switches that way.

So this reflects bitrot in that legacy code, for x86/ia64: kernels with
HPET support configured (e.g.  for a clocksource) can't get IRQs from the
legacy RTC driver unless they really have HPET hardware.  (The obvious
workaround is to not use the legacy RTC driver on those platforms when you
configure HPET ...  unless you know the target really has a HPET.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>