arc: 1msec tick gives more stable scheduling

I notice that many of the other boards here use 1msec for the tick.
I notice also that when switching to unified kernel, scheduling based
on time has a lot more jitter with a 5msec tick.

I think a better default is 1000 ticks per second for em_starterkit.

Change-Id: Icc93345762dbea7d71ca9f4735bcf73f75cde273
Signed-off-by: Chuck Jordan <cjordan@synopsys.com>