modules: rename packages/kernel_modules to packages/lkmc

Then inside, split packages/lkmc into kernel_modules and userland,
to keep userland out of the kernel_modules parent path, which makes no
sense.

Copy built modules and userland to the output rootfs overlay.

Document Linux distro tradeoffs.

build-buildroot

@@ -22,7 +22,6 @@ defaults = {
     'kernel_config_fragment': [],
     'kernel_custom_config_file': None,
     'kernel_modules': False,
-    'no_kernel_modules': False,
     'linux_reconfigure': False,
     'no_all': False,
     'nproc': None,
@@ -96,7 +95,9 @@ Still uses options explicitly passed with `-C` and `-c` on top of it.
     )
     kernel_module_group.add_argument(
         '-k', '--kernel-modules', default=defaults['kernel_modules'], action='store_true',
-        help='Reconfigure and rebuild the kernel modules package'
+        help='''Reconfigure and rebuild the kernel modules package.
+Force --build-linux to true, since building the modules requires building Linux.
+'''
     )
     parser.add_argument(
         '--no-all', default=defaults['no_all'], action='store_true',
@@ -130,8 +131,8 @@ def main(args, extra_args=None):
         os.makedirs(common.out_dir, exist_ok=True)
         extra_make_args = args.extra_make_args.copy()
         if args.kernel_modules:
-            assert(args.build_linux)
-            extra_make_args.append('kernel_modules-reconfigure')
+            args.build_linux = True
+            extra_make_args.append('lkmc-reconfigure')
         if args.linux_reconfigure:
             extra_make_args.append('linux-reconfigure')
         if args.gem5:
@@ -149,12 +150,6 @@ def main(args, extra_args=None):
 
         # Configure.
         if not args.skip_configure:
-            # Initial make configure.
-            # TODO port and test.
-            #cd "${common_buildroot_src_dir}"
-            #for p in $(find "${common_root_dir}/patches/buildroot/" -maxdepth 1 -name '*.patch' -print); do
-            #  patch -N -r - -p 1 < "$p" || :
-            #done
             br2_external_dirs = []
             packages_dir = os.path.join(common.root_dir, 'packages')
             for package_dir in os.listdir(packages_dir):
@@ -197,7 +192,7 @@ def main(args, extra_args=None):
                         path_relative_to_buildroot(os.path.join(common.root_dir, 'user_table'))),
                 ])
                 if args.kernel_modules:
-                    buildroot_configs.append('BR2_PACKAGE_KERNEL_MODULES=y')
+                    buildroot_configs.append('BR2_PACKAGE_LKMC=y')
                 if args.gem5:
                     buildroot_configs.append('BR2_PACKAGE_GEM5=y')
                 if args.initramfs: