dt-bindings: xilinx: Remove description for SystemACE

SystemACE driver has been removed by commit 2907f851f64a ("xsysace: Remove
SYSACE driver") that's why there is no reason to keep description in
xilinx.txt file.

Signed-off-by: Michal Simek <[e-mail]>
Link: https://lore.kernel.org/r/7ed7[e-mail]
Signed-off-by: Rob Herring (Arm) <[e-mail]>

Documentation/devicetree/bindings/xilinx.txt

···
                                            Default is <d#1024 d#480>.
        - rotate-display (empty) : rotate display 180 degrees.
 
-      ii) Xilinx SystemACE
-
-      The Xilinx SystemACE device is used to program FPGAs from an FPGA
-      bitstream stored on a CF card.  It can also be used as a generic CF
-      interface device.
-
-      Optional properties:
-       - 8-bit (empty) : Set this property for SystemACE in 8 bit mode
-
       iii) Xilinx EMAC and Xilinx TEMAC
 
       Xilinx Ethernet devices.  In addition to general xilinx properties