ARM: mx6: ddr: Factor out SDQS configuration code

ARM: mx6: ddr: Factor out SDQS configuration code

Pull out the code turning SDQS pullups on and off into a separate
function, since it is replicated in two places in the code and it
is the single place in the entire function which is SoC dependent.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eric Nelson <eric@nelint.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Eric Nelson <eric@nelint.com>