Mea culpa on the pmax_3max_subr.h. It includes the declarations you're
missing and seeing warnings for. It's in the tree now and will show up
in tomorrows sup.

mips_hardware_intr is a function pointer declared in
sys/arch/mips/include/intr.h. You should be pulling it in via
<machine/intr.h>; sys/arch/pmax/include/intr.h incldues the mips
version.  

I just checked in a update to pmax/include/intr.h which provides IPL_*
constants.  (The TC glue code and definitions for the pmax port not
having IPL_* can be blown away.)  I double-checked: that version
definitely includes the right stuff to get mips_hardware_intr declared.