soc/ite/ec: it51xxx: Add a new SoC variant it51526bw

1. Add it51526bw SoC variant to it51xxx SoC series.
2. Create the .dtsi file with adjusted flash size for 512Kb (default = 1M).

Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>

soc/ite/ec/it51xxx/Kconfig.soc

@@ -15,8 +15,13 @@ config SOC_IT51526AW
 	bool
 	select SOC_IT51XXX
 
+config SOC_IT51526BW
+	bool
+	select SOC_IT51XXX
+
 config SOC_SERIES
 	default "it51xxx" if SOC_SERIES_IT51XXX
 
 config SOC
 	default "it51526aw" if SOC_IT51526AW
+	default "it51526bw" if SOC_IT51526BW

soc/ite/ec/soc.yml

@@ -20,3 +20,4 @@ family:
       - name: it51xxx
         socs:
           - name: it51526aw
+          - name: it51526bw