nexys_base: reactivate refresh (now fixed in litedram)
nexys_base: reactivate refresh (now fixed in litedram)

mithro/HDMI2USB-litex-firmware,cr1901/HDMI2USB-litex-firmware,cr1901/HDMI2USB-litex-firmware,cr1901/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware,cr1901/HDMI2USB-litex-firmware,mithro/HDMI2USB-litex-firmware