rpi-base: fix make_dtb_boot_files() for raspberrypi3-64

Building the stock wic image for raspberrypi3-64 failed to find dtbs listed in
IMAGE_BOOT_FILES. This patch updates the make_dtb_boot_files() function to
account for dtbs listed in KERNEL_DEVICETREE that do include a path prefix:
this is the case for things like broadcom/bcm2710-rpi-3-b.dtb (the dts dir
layout in the kernel sources is different for arm64). Use the same approach
already used for overlays/ dir. While at it also fix a typo in dtb overlay
code path comments.

Signed-off-by: Andrea Galbusera <gizero@gmail.com>

conf/machine/include/rpi-base.inc

@@ -61,16 +61,17 @@ def make_dtb_boot_files(d):
 
     def transform(dtb):
         if dtb.endswith('dtb'):
-            # eg: bcm2708-rpi-b.dtb has:
+            # eg: whatever/bcm2708-rpi-b.dtb has:
             #     DEPLOYDIR file: ${KERNEL_IMAGETYPE}-bcm2708-rpi-b.dtb
             #     destination: bcm2708-rpi-b.dtb
-            src = '{}-{}'.format(imgtyp, dtb)
-            dst = dtb
+            base = os.path.basename(dtb)
+            src = '{}-{}'.format(imgtyp, base)
+            dst = base
             return '{};{}'.format(src, dst)
         elif dtb.endswith('dtbo'):
             # overlay dtb:
             # eg: overlays/hifiberry-amp.dtbo has:
-            #     DEPLOYDIR file: ${KERNEL_IMAGETYPE}-hifiberry-amp.dtbp
+            #     DEPLOYDIR file: ${KERNEL_IMAGETYPE}-hifiberry-amp.dtbo
             #     destination: overlays/hifiberry-amp.dtbo
             base = os.path.basename(dtb)
             src = '{}-{}'.format(imgtyp, base)