dt-bindings: serial: lpuart: add ls1028a compatibility

Add the LS1028A SoC compatibility string to the lpuart devicetree
bindings documentation.
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20200307091302.14881-1-michael@walle.ccSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Documentation/devicetree/bindings/serial/fsl-lpuart.txt

@@ -6,6 +6,8 @@ Required properties:
     on Vybrid vf610 SoC with 8-bit register organization
   - "fsl,ls1021a-lpuart" for lpuart compatible with the one integrated
     on LS1021A SoC with 32-bit big-endian register organization
+  - "fsl,ls1028a-lpuart" for lpuart compatible with the one integrated
+    on LS1028A SoC with 32-bit little-endian register organization
   - "fsl,imx7ulp-lpuart" for lpuart compatible with the one integrated
     on i.MX7ULP SoC with 32-bit little-endian register organization
   - "fsl,imx8qxp-lpuart" for lpuart compatible with the one integrated
@@ -15,10 +17,10 @@ Required properties:
 - reg : Address and length of the register set for the device
 - interrupts : Should contain uart interrupt
 - clocks : phandle + clock specifier pairs, one for each entry in clock-names
-- clock-names : For vf610/ls1021a/imx7ulp, "ipg" clock is for uart bus/baud
-  clock. For imx8qxp lpuart, "ipg" clock is bus clock that is used to access
-  lpuart controller registers, it also requires "baud" clock for module to
-  receive/transmit data.
+- clock-names : For vf610/ls1021a/ls1028a/imx7ulp, "ipg" clock is for uart
+  bus/baud clock. For imx8qxp lpuart, "ipg" clock is bus clock that is used
+  to access lpuart controller registers, it also requires "baud" clock for
+  module to receive/transmit data.
 
 Optional properties:
 - dmas: A list of two dma specifiers, one for each entry in dma-names.