Exynos5250: add a microsecond timer

Add a microsecond timer, its declaration, the function to start it,
and its usage.  To start it, one calls timer_start().  From that point
on, one can call timer_us() to find microseconds since the timer was
started.

We show its use in the bootblock. You want it started very early.

Finally, the delay.h change having been (ironically) delayed, we
create time.h and have it hold one declaration, for the timer_us() and
timer_start() prototype.

We feel that these two functions should become the hardware specific
functions, allowing us to finally move udelay() into src/lib where it
belongs.

Change-Id: I19cbc2bb0089a3de88cfb94276266af38b9363c5
Signed-off-by: Ronald G. Minnich <rminnich@gmail.com>
Reviewed-on: http://review.coreboot.org/3073
Tested-by: build bot (Jenkins)

src/arch/armv7/lib/Makefile.inc

@@ -1,6 +1,5 @@
 #FIXME: cache_v7 and cache-cp15 will go away eventually
 
-bootblock-y += syslib.c
 bootblock-$(CONFIG_EARLY_CONSOLE) += early_console.c
 bootblock-y += cache.c
 
@@ -13,7 +12,6 @@ ramstage-y += div0.c
 #ramstage-y += interrupts.c
 #ramstage-y += memcpy.S
 #ramstage-y += memset.S
-ramstage-y += syslib.c
 ramstage-y += cache.c
 ramstage-y += mmu.c