Implement new accessor, sysmgr_get_pinmux_table(), used to obtain pinmux
table and it's size from the QTS-generated pinmux_config.c. The target
here is again to get rid of poluting global namespace by including the
pinmux_config.h into it.

Furthermore, the pinmux_config.h declares some CONFIG_HPS_* macros,
which are explicitly useless to us in U-Boot. Instead, U-Boot does
use DT to detect exactly these configuration options. This patch
makes sure that while this QTS-generated file can stay in the tree,
these obscure macros do not ooze into the namespace anymore.

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