Linux 6.10 compat: fix rpm-kmod and builtin

The 6.10 kernel broke our rpm-kmod builds.  The 6.10 kernel really
wants the source files in the same directory as the object files.
This workaround makes rpm-kmod work again.  It also updates
the builtin kernel codepath to work correctly with 6.10.

See kernel commits:

b1992c3772e6 kbuild: use $(src) instead of $(srctree)/$(src) for source
                     directory
9a0ebe5011f4 kbuild: use $(obj)/ instead of $(src)/ for common pattern
                     rules

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Tony Hutter <hutter2@llnl.gov>
Closes #16439
Closes #16450

module/Kbuild.in

@@ -16,8 +16,8 @@ src = @abs_srcdir@
 obj = @abs_builddir@
 else
 zfs_include = $(srctree)/include/zfs
-icp_include = $(srctree)/$(src)/icp/include
-zstd_include = $(srctree)/$(src)/zstd/include
+icp_include = $(src)/icp/include
+zstd_include = $(src)/zstd/include
 ZFS_MODULE_CFLAGS += -include $(zfs_include)/zfs_config.h
 endif