linux: select proper defconfig on PowerPC

The handling of BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG is currently
not doing a proper job: it is selecting ppc64le_defconfig if
BR2_powerpc64le, and using the default of "defconfig" for everything
else.

However:

- Since upstream commit 22f17b02f88b48c01d3ac38d40d2b0b695ab2d10,
  which landed in Linux 6.8, the default defconfig is
  ppc64le_defconfig and no longer ppc64_defconfig. This means that
  despite the condition in linux.mk, we are in fact now always
  building ppc64le_defconfig.

- It doesn't handle the 32-bit case, as a 64-bit defconfig gets used
  by default. This causes build failures in the autobuilders.

To fix this we explicitly handle BR2_powerpc64le, BR2_powerpc64 and
BR2_powerpc, and use appropriate defconfigs for each case.

Fixes:

  http://autobuild.buildroot.net/results/c15eaf2e7455aa265cc045e6d8be7cac5348d925/ (powerpc)

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>
(cherry picked from commit 82326a3d8392d02f53c47bdaed21ff8012a6d978)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

linux/linux.mk

@@ -343,6 +343,10 @@ LINUX_KCONFIG_DEFCONFIG = $(call qstrip,$(BR2_LINUX_KERNEL_DEFCONFIG))_defconfig
 else ifeq ($(BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG),y)
 ifeq ($(BR2_powerpc64le),y)
 LINUX_KCONFIG_DEFCONFIG = ppc64le_defconfig
+else ifeq ($(BR2_powerpc64),y)
+LINUX_KCONFIG_DEFCONFIG = ppc64_defconfig
+else ifeq ($(BR2_powerpc),y)
+LINUX_KCONFIG_DEFCONFIG = ppc_defconfig
 else
 LINUX_KCONFIG_DEFCONFIG = defconfig
 endif