kbuild: rpm-pkg: disable kernel-devel package when cross-compiling

Since commit f1d87664 ("kbuild: cross-compile linux-headers package
when possible"), 'make binrpm-pkg' may attempt to cross-compile the
kernel-devel package, but it fails under certain circumstances.

For example, when CONFIG_MODULE_SIG_FORMAT is enabled on openSUSE
Tumbleweed, the following command fails:

  $ make ARCH=arm64 CROSS_COMPILE=aarch64-suse-linux- binrpm-pkg
      [ snip ]
  Rebuilding host programs with aarch64-suse-linux-gcc...
    HOSTCC  /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/kallsyms
    HOSTCC  /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sorttable
    HOSTCC  /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/asn1_compiler
    HOSTCC  /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sign-file
  /home/masahiro/ref/linux/rpmbuild/BUILDROOT/kernel-6.12.0_rc4-1.aarch64/usr/src/kernels/6.12.0-rc4/scripts/sign-file.c:25:10: fatal error: openssl/opensslv.h: No such file or directory
     25 | #include <openssl/opensslv.h>
        |          ^~~~~~~~~~~~~~~~~~~~
  compilation terminated.

I believe this issue is less common on Fedora because the disto's cross-
compilier cannot link user-space programs. Hence, CONFIG_CC_CAN_LINK is
unset.

On Fedora 40, the package information explains this limitation clearly:

  $ dnf info gcc-aarch64-linux-gnu
      [ snip ]
  Description  : Cross-build GNU C compiler.
               :
               : Only building kernels is currently supported.  Support for cross-building
               : user space programs is not currently provided as that would massively multiply
               : the number of packages.

Anyway, cross-compiling RPM packages is somewhat challenging.

This commit disables the kernel-devel package when cross-compiling
because I did not come up with a better solution.

Fixes: f1d87664 ("kbuild: cross-compile linux-headers package when possible")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>