Blackfin arch: fix bugs and unify BFIN_KERNEL_CLOCK option

 - remove duplicated code and headers
 - add option allowing arbitrary SDRAM/DDR Timing parameters.
 - mark automatically calculated timings as EXPERIMENTAL
 - fix comment header block

Related to BUGs:
 - kernel boot up fails with CONFIG_BFIN_KERNEL_CLOCK item on.
 - kernel does not boot if re-program clocks

[ Mike Frysinger <vapier.adi@gmail.com>
 - fix comment header
 - mark do_sync static
 - document the DMA shutdown
 - simplify SIC_IWR handling
 - fix ANOMALY_05000265 handling to work as intended ]

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>