blackfin: Correct early serial mess output in BYPASS boot mode.

blackfin: Correct early serial mess output in BYPASS boot mode.

The early serial should not be configured again in initcode() for BYPASS
boot mode and in start() for the other LDR boot modes.

In BYPASS boot mode, the start up code is located in Nor flash address other
than the DRAM address defined in link script. The code embedded string can't
be addressed by its compile time symbol. Calculate it according to the flash
offset.

Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>