arm64: dts: Move BCM4908 dts to bcmbca folder

As part of ARCH_BCM4908 to ARCH_BCMBCA migration, move the BCM4908 dts
files to bcmbca folder and use CONFIG_ARCH_BCMBCA to build all the
BCM4908 board dts. Delete bcm4908 folder and its makefile as well.
Signed-off-by: William Zhang <william.zhang@broadcom.com>
Link: https://lore.kernel.org/r/20220803175455.47638-5-william.zhang@broadcom.comSigned-off-by: Florian Fainelli <f.fainelli@gmail.com>

arch/arm64/boot/dts/broadcom/Makefile

@@ -8,7 +8,6 @@ dtb-$(CONFIG_ARCH_BCM2835) += bcm2711-rpi-400.dtb \
 			      bcm2837-rpi-cm3-io3.dtb \
 			      bcm2837-rpi-zero-2-w.dtb
 
-subdir-y	+= bcm4908
 subdir-y	+= bcmbca
 subdir-y	+= northstar2
 subdir-y	+= stingray

arch/arm64/boot/dts/broadcom/bcm4908/Makefile

-# SPDX-License-Identifier: GPL-2.0
-dtb-$(CONFIG_ARCH_BCM4908) += bcm4906-netgear-r8000p.dtb
-dtb-$(CONFIG_ARCH_BCM4908) += bcm4906-tplink-archer-c2300-v1.dtb
-dtb-$(CONFIG_ARCH_BCM4908) += bcm4908-asus-gt-ac5300.dtb
-dtb-$(CONFIG_ARCH_BCM4908) += bcm4908-netgear-raxe500.dtb

arch/arm64/boot/dts/broadcom/bcmbca/Makefile

 # SPDX-License-Identifier: GPL-2.0
 dtb-$(CONFIG_ARCH_BCMBCA) += \
+				bcm4906-netgear-r8000p.dtb \
+				bcm4906-tplink-archer-c2300-v1.dtb \
+				bcm4908-asus-gt-ac5300.dtb \
+				bcm4908-netgear-raxe500.dtb \
 				bcm4912-asus-gt-ax6000.dtb \
 				bcm94912.dtb \
 				bcm963158.dtb \