ARM: AM4372: Update EMIF registers for DDR3

Updating EMIF_PHY_CTRL and adding EMIF_READ_WRITE_EXECUTION_THRESHOLD
registers.
In EMIF_PHY_CTRL:
Updating [4:0]READ_LATENCY to 8, because at higher frequencies like
400MHz the read latency expected will be CL+3 as per tests from HW
folks.
Clearing [19]PHY_DIS_CALIB_RST bit as this is used onl for debug
purpose. With out this resume is not working(Still waiting for PHY team
to come back for better explanation).

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>