arm: omap4: Fix SDRAM AUTO DETECTION

Commit "86021143 omap: emif: configure emif only when required"
breaks SDRAM_AUTO_DETECTION.
The issue is dmm_init() depends on emif_sizes[](SDRAM Auto detection)
done in do_sdram_init(). The above commit moves dmm_init() above
do_sdram_init() because of which dmm_init() uses uninitialized
emif_sizes[].
So instead of using global emif_sizes[], get sdram details locally
and calculate emif sizes.

Reported-by: Michael Cashwell <mboards@prograde.net>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>