rtc/ia64: remove legacy efirtc driver

There are two EFI RTC drivers, the original drivers/char/efirtc.c
driver and the more modern drivers/rtc/rtc-efi.c.

Both implement the same interface, but the new one does so
in a more portable way.

Move everything over to that one and remove the old one.

Cc: linux-ia64@vger.kernel.org
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Stephane Eranian <eranian@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20200226224322.187960-1-alexandre.belloni@bootlin.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>