dm: ddr: socfpga: fix gen5 ddr driver to not use bss

This driver uses bss from SPL board_init_f(). Change it to move all the
data from bss to a common struct allocated on the stack (64 byte).

In addition to saving 28 bytes of bss, the code even gets 264 bytes
smaller.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>