ARM: davinci: da850: Add ti-aemif lookup for clock matching

The davinci boards don't have their clocks in DT yet and getting a clock
will fail, unless registering them as clk_lookups. This registers the
aemif clock for the ti-aemif memory driver.

The current aemif lookup entry resolving to the same clock:
    'CLK(NULL,               "aemif",        &aemif_clk)'
is currently used by davinci_nand and remains for non-DT and backward
compatibility.

Currently the davinci boards only configure the AEMIF in case of non-DT
boot, via some code in mach-davinci.
This change will allow DT-based davinci platforms to do the same, via
the ti-aemif memory driver code.

Signed-off-by: Karl Beldan <kbeldan@baylibre.com>
[nsekhar@ti.com: reworded commit message]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>