ARM: am33xx: Always inhibit init/refresh during DDR phy init

ARM: am33xx: Always inhibit init/refresh during DDR phy init

A couple of commits have modified the am33xx/am437x ddr2/ddr3
initialization path to fix certain issues, but have had the side effect
of causing L3 noc errors during initialization. The two commits are:

69b918 "am33xx,ddr3: fix ddr3 sdram configuration"
fc46ba "arm: am437x: Enable hardware leveling for EMIF"

The EMIF_REG_INITREF_DIS_MASK bit still needs to be set for all
platforms. This delays initialization and refresh until a later stage.
The 500us timer can be programmed for platforms that require it
and for platforms that don't require it. It is currently hardcoded
for 400MHz systems. For systems with a higher memory frequency
this needs to be a larger value, and for systems with a lower
memory frequency this can be a lower value. This can be
considered a separate issue and corrected in a later commit.

Signed-off-by: Russ Dill <Russ.Dill@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>