Fix the handling of MMU type in the AP entry code.  The ARM_MMU_V6/V7
symbols are always #defined to 0 or 1, so use #if SYM not #if defined(SYM).
Also, it helps if you include the header file that defines the symbols.


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270862 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Allow the make_dtb script to work outside of a "make buildkernel" context
by setting MACHINE from uname -m if it's not set already.

Reviewed by:	imp, tuexen


git-svn-id: svn+ssh://svn.freebsd.org/base/head@270863 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f