kbuild: rpm-pkg: fix build error with CONFIG_MODULES=n

When CONFIG_MODULES is disabled, 'make (bin)rpm-pkg' fails:

  $ make allnoconfig binrpm-pkg
    [ snip ]
  error: File not found: .../linux/rpmbuild/BUILDROOT/kernel-6.10.0_rc3-1.i386/lib/modules/6.10.0-rc3/kernel
  error: File not found: .../linux/rpmbuild/BUILDROOT/kernel-6.10.0_rc3-1.i386/lib/modules/6.10.0-rc3/modules.order

To make it work irrespective of CONFIG_MODULES, this commit specifies
the directory path, /lib/modules/%{KERNELRELEASE}, instead of individual
files.

However, doing so would cause new warnings:

  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.alias
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.alias.bin
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.builtin.alias.bin
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.builtin.bin
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.dep
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.dep.bin
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.devname
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.softdep
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.symbols
  warning: File listed twice: /lib/modules/6.10.0-rc3-dirty/modules.symbols.bin

These files exist in /lib/modules/%{KERNELRELEASE} and are also explicitly
marked as %ghost.

Suppress depmod because depmod-generated files are not packaged.

Fixes: 615b3a3d

 ("kbuild: rpm-pkg: do not include depmod-generated files")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>