Introduce accessor iocsr_get_config_table() for retrieving IOCSR config
tables. This patch is again trimming down the namespace polution.

The IOCSR config tables are used only by scan manager, they are generated
by qts and are board specific. Before this patch, the approach to use
these tables in scan manager was to define an extern variable to silence
the compiler and compile board-specific iocsr_config.c into U-Boot which
defined those extern variables. Furthermore, since these are tables and
the scan manager needs to know the size of those tables, iocsr_config.h
is included build-wide.

This patch wraps all this into a single accessor which takes the scan
chain ID and returns pointer to the table and it's size. All this is
wrapped in wrap_iocsr_config.c board-specific file. The file includes
the iocsr_config.c (!) to access the original tables and transitively
iocsr_config.h . It is thus no longer necessary to include iocsr_config.h
build-wide and the namespace polution is trimmed some more.

Signed-off-by: Marek Vasut <marex@denx.de>