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/Makefile b/arch/arm/dts/Makefile
index 1fb8f83..8d1e969 100644
--- a/arch/arm/dts/Makefile
+++ b/arch/arm/dts/Makefile
@@ -1164,9 +1164,6 @@
 	bcm2837-rpi-cm3-io3.dtb \
 	bcm2711-rpi-4-b.dtb
 
-dtb-$(CONFIG_ARCH_BCM68360) += \
-	bcm968360bg.dtb
-
 dtb-$(CONFIG_ARCH_BCM6753) += \
 	bcm96753ref.dtb
 
@@ -1200,7 +1197,8 @@
 dtb-$(CONFIG_BCM6846) += \
 	bcm96846.dtb
 dtb-$(CONFIG_BCM6856) += \
-	bcm96856.dtb
+	bcm96856.dtb \
+	bcm968360bg.dtb
 dtb-$(CONFIG_BCM6878) += \
 	bcm96878.dtb