Blackfin: drop per-cpu loops_per_jiffy tracking

On Blackfin SMP, a per-cpu loops_per_jiffy is pointless since both cores
always run at the same CCLK.  In addition, the current implementation has
flaws since the main consumer for loops_per_jiffy (asm/delay.h) uses the
global kernel loops_per_jiffy and not the per_cpu one.  So punt all of the
per-cpu handling and go back to the global shared one.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>