Merge branch 'builtin-clean'

Support in-tree builtin module building.

These commits add support for compiling the SPL module as a built-in
kernel module by copying the module code into the kernel source tree.
Here's the procedure:

• Create your kernel configuration (.config file) as usual. This has to be done first so that SPL's configure script is able to detect kernel features correctly.
• Run make prepare scripts inside the kernel source tree.
• Run ./configure --enable-linux-builtin --with-linux=/usr/src/linux-... inside the SPL directory.
• Run ./copy-builtin /usr/src/linux-... inside the SPL directory.
• In the kernel source tree, enable the CONFIG_SPL option (e.g. using make menuconfig).
• Build the kernel as usual.

SPL module parameters can be set at boot time using the following syntax
on the kernel command line: spl.parameter_name=parameter_value.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue zfsonlinux/zfs#851