alpha: fix RTC on marvel

Unlike other alphas, marvel doesn't have real PC-style CMOS clock hardware
- RTC accesses are emulated via PAL calls.  Unfortunately, for unknown
reason these calls work only on CPU #0.  So current implementation for
arbitrary CPU makes CMOS_READ/WRITE to be executed on CPU #0 via IPI.
However, for obvious reason this doesn't work with standard
get/set_rtc_time() functions, where a bunch of CMOS accesses is done with
disabled interrupts.

Solved by making the IPI calls for entire get/set_rtc_time() functions,
not for individual CMOS accesses.  Which is also a lot more effective
performance-wise.

The patch is largely based on the code from Jay Estabrook.
My changes:
- tweak asm-generic/rtc.h by adding a couple of #defines to
  avoid a massive code duplication in arch/alpha/include/asm/rtc.h;
- sys_marvel.c: fix get/set_rtc_time() return values (Jay's FIXMEs).

NOTE: this fixes *only* LIB_RTC drivers.  Legacy (CONFIG_RTC) driver
wont't work on marvel.  Actually I think that we should just disable
CONFIG_RTC on alpha (maybe in 2.6.30?), like most other arches - AFAIK,
all modern distributions use LIB_RTC anyway.

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/include/asm/rtc.h

@@ -1,9 +1,15 @@
 #ifndef _ALPHA_RTC_H
 #define _ALPHA_RTC_H
 
-/*
- * Alpha uses the default access methods for the RTC.
- */
+#if defined(CONFIG_ALPHA_GENERIC)
+# define get_rtc_time		alpha_mv.rtc_get_time
+# define set_rtc_time		alpha_mv.rtc_set_time
+#else
+# if defined(CONFIG_ALPHA_MARVEL) && defined(CONFIG_SMP)
+#  define get_rtc_time		marvel_get_rtc_time
+#  define set_rtc_time		marvel_set_rtc_time
+# endif
+#endif
 
 #include <asm-generic/rtc.h>