ddr: altera: sdram: Clean up set_sdr_ctrlcfg()

Get rid of the constant clrsetbits_le32(), instead prepare the whole
content of the register once and write it at the end of the function.
The big plan here is to remove all the CONFIG_HPS_SDR_ macros, hide
them in QTS compatibility layer in board implementation and pass only
a small structure into the driver.

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