ARM: OMAP4+: emif: Detect SDRAM from SDRAM config register

Now SDRAM initialization is done on the basis of omap revision.
Instead this should be done on basis of SDRAM type read from
EMIF_SDRAM_CONFIG register. This will be helpful to avoid
unnessecary cpu checks for new boards

Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@ti.com>