This simplifies setup by remove the unneeded RAM voltage checking.
According to the spec, DDR3L RAM has to work using 1.5V, see
https://en.wikipedia.org/wiki/DDR3_SDRAM#DDR3L_and_DDR3U_extensions.
Coreboot simply doesn't always implement changing voltage, which
can never prevent RAM from working though.
Closes#50Fixes#38