ARM: dts: TS-4800: use weim IP to map the FPGA

Previously, the device tree mapped the FPGA like any other IPs inside
the SoC, but it is actually mapped through the WEIM (Wireless External
Interface Module). This patch updates the device tree to make use of it.

About the timings: in the image provided by the manufacturer, only
CS0GCR1 is changed. The other values are the default ones, but the WEIM
bindings expect them to be all explicitly set in the device tree, so I
just put the default values in the dt.

Signed-off-by: Damien Riegel <damien.riegel@savoirfairelinux.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>