arm: bcmbca: remove bcm68360 support under CONFIG_ARCH_BCM68360

BCM68360 is a variant within the BCM6856 chip family. Now that BCM6856
is supported under CONFIG_ARCH_BCMBCA and CONFIG_BCM6856, remove the
original ARCH_BCM68360 support and migrate its configuration and dts
settings. This includes:
  - Remove the bcm968360bg board folder. It is replaced by the generic
    bcmbca board folder.
  - Merge the 68360.dtsi setting to the new 6856.dtsi file. Update board
    dts with the new compatible string.
  - Merge broadcom_bcm968360bg.h setting to the new bcm96856.h file.
  - Remove bcm968360bg_ram_defconfig as a basic config version of
    bcm96856_defconfig is now added.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Reviewed-by: Philippe Reynes <philippe.reynes@softathome.com>
diff --git a/arch/arm/dts/bcm968360bg.dts b/arch/arm/dts/bcm968360bg.dts
index c060294..6f1090a 100644
--- a/arch/arm/dts/bcm968360bg.dts
+++ b/arch/arm/dts/bcm968360bg.dts
@@ -5,11 +5,11 @@
 
 /dts-v1/;
 
-#include "bcm68360.dtsi"
+#include "bcm6856.dtsi"
 
 / {
-	model = "Broadcom bcm68360bg";
-	compatible = "broadcom,bcm68360bg", "brcm,bcm68360";
+	model = "Broadcom BCM968360BG Reference Board";
+	compatible = "brcm,bcm968360bg", "brcm,bcm6856", "brcm,bcmbca";
 
 	aliases {
 		serial0 = &uart0;