[MIPS] Fixup migration to GENERIC_TIME

Since we already moved to GENERIC_TIME, we should implement alternatives
of old do_gettimeoffset routines to get sub-jiffies resolution from
gettimeofday().  This patch includes:

 * MIPS clocksource support (based on works by Manish Lachwani).
 * remove unused gettimeoffset routines and related codes.
 * remove unised 64bit do_div64_32().
 * simplify mips_hpt_init. (no argument needed, __init tag)
 * simplify c0_hpt_timer_init. (no need to write to c0_count)
 * remove some hpt_init routines.
 * mips_hpt_mask variable to specify bitmask of hpt value.
 * convert jmr3927_do_gettimeoffset to jmr3927_hpt_read.
 * convert ip27_do_gettimeoffset to ip27_hpt_read.
 * convert bcm1480_do_gettimeoffset to bcm1480_hpt_read.
 * simplify sb1250 hpt functions. (no need to subtract and shift)
    
Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/sgi-ip27/ip27-timer.c b/arch/mips/sgi-ip27/ip27-timer.c
index 4e870fc..c965705 100644
--- a/arch/mips/sgi-ip27/ip27-timer.c
+++ b/arch/mips/sgi-ip27/ip27-timer.c
@@ -134,13 +134,6 @@
 	irq_exit();
 }
 
-unsigned long ip27_do_gettimeoffset(void)
-{
-	unsigned long ct_cur1;
-	ct_cur1 = REMOTE_HUB_L(cputonasid(0), PI_RT_COUNT) + CYCLES_PER_JIFFY;
-	return (ct_cur1 - ct_cur[0]) * NSEC_PER_CYCLE / 1000;
-}
-
 /* Includes for ioc3_init().  */
 #include <asm/sn/types.h>
 #include <asm/sn/sn0/addrs.h>
@@ -248,12 +241,17 @@
 	setup_irq(irqno, &rt_irqaction);
 }
 
+static unsigned int ip27_hpt_read(void)
+{
+	return REMOTE_HUB_L(cputonasid(0), PI_RT_COUNT);
+}
+
 void __init ip27_time_init(void)
 {
+	mips_hpt_read = ip27_hpt_read;
+	mips_hpt_frequency = CYCLES_PER_SEC;
 	xtime.tv_sec = get_m48t35_time();
 	xtime.tv_nsec = 0;
-
-	do_gettimeoffset = ip27_do_gettimeoffset;
 }
 
 void __init cpu_time_init(void)