Remove obsolete compatibility glue and improve firewire code readability.

Commit my version of style(9) pass over the firewire code. Now that
other people have started changing the code carrying this is as a
local patch is not longer a viable option.

MFC after:	1 month
Do not pass whole descriptor block size as align to fwdma_malloc_multiseg

Do not pass wrong alignment value to fwdma_malloc_multiseg and ultimately
to contigalloc. In addition to being wrong, this causes insta-panic in
certain cases due to safety assertion - the alignment is required to be
the power of two and the value we calculate here seldom is.

MFC after:  1 month
Disable the makeoption with MFS_IMAGE= set as we don't ship that file
and it thus breaks the default build.   You can still use various other
ways (tools) to embedd the image after the kernel build.