sdcard_image-rpi.bbclass: Remove redundant RPI_KERNEL_VERSION

The value of the RPI_KERNEL_VERSION can change between None and the
kernel version which can result in taskhash mismatch errors while
building images.

The taskhash mismatch errors can be reproduced using:
bitbake -c cleansstate virtual/kernel core-image-minimal && bitbake core-image-minimal

The get_dts() and split_overlays() functions are modified so that the
kernel version argument is optional. If the version is not supplied to
these functions, they will fallback to the Python equivalent of the
expression used for RPI_KERNEL_VERSION.

Signed-off-by: Jonathan Liu <net147@gmail.com>
Signed-off-by: Khem Raj <raj.khem@gmail.com>

classes/linux-raspberrypi-base.bbclass

@@ -1,6 +1,6 @@
 inherit linux-kernel-base
 
-def get_dts(d, ver):
+def get_dts(d, ver=None):
     import re
 
     staging_dir = d.getVar("STAGING_KERNEL_BUILDDIR", True)
@@ -32,7 +32,7 @@ def get_dts(d, ver):
     return dts
 
 
-def split_overlays(d, ver, out):
+def split_overlays(d, out, ver=None):
     dts = get_dts(d, ver)
     if out:
         overlays = oe.utils.str_filter_out('\S+\-overlay\.dtb$', dts, d)