ARM: OMAP2+: gpmc: Keep Chip Select disabled while configuring it

As per the OMAP reference manual [1], the Chip Select must be
disabled (i.e. CSVALID is 0) while configuring any of the
Chip select parameters.

[1] - 10.1.5.1 Chip-Select Base Address and Region Size Configuration
http://www.ti.com/lit/pdf/swpu177



Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>