ARM: dts: dra74x: Fix iodelay configuration for mmc3

According to the latest am572x[1] and dra74x[2] data manuals, mmc3
default, hs, sdr12 and sdr25 modes use iodelay values given in
MMC3_MANUAL1. Set the MODE_SELECT bit for these so that manual mode is
selected and correct iodelay values can be configured.

[1] http://www.ti.com/lit/ds/symlink/am5728.pdf
[2] http://www.ti.com/lit/ds/symlink/dra746.pdf

Signed-off-by: Faiz Abbas <faiz_abbas@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>