rtc: make HPET_RTC_IRQ track HPET_EMULATE_RTC

More Kconfig tweaks related to the legacy PC RTC code:

- Describe the legacy PC RTC driver as such ... it's never quite
been clear that this driver is for PC RTCs, and now it's fair
to call this the "legacy" driver.

- Force it to understand about HPET stealing its IRQs ... kernel
code does this always when HPET is in use, there should be no
option for users to goof up the config.

This seems to fix kernel bugzilla #10729.

Signed-off-by: David Brownell <[e-mail]>
Cc: Maxim Levitsky <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/char/Kconfig

···
 if RTC_LIB=n
 
 config RTC
-	tristate "Enhanced Real Time Clock Support"
+	tristate "Enhanced Real Time Clock Support (legacy PC RTC driver)"
 	depends on !PPC && !PARISC && !IA64 && !M68K && !SPARC && !FRV \
 			&& !ARM && !SUPERH && !S390 && !AVR32
 	---help---
···
 	  non-periodic and/or periodic.
 
 config HPET_RTC_IRQ
-	bool "HPET Control RTC IRQ" if !HPET_EMULATE_RTC
-	default n
-	depends on HPET
+	bool
+	default HPET_EMULATE_RTC
+	depends on RTC && HPET
 	help
 	  If you say Y here, you will disable RTC_IRQ in drivers/char/rtc.c. It
 	  is assumed the platform called hpet_alloc with the RTC IRQ values for