Int 21 Fn 251C  P - Phar Lap 386/dos-extender Vmm V2.1c+ - Free Physical   [E]

   AX = 251Ch
   BH = preservation flag (00h preserve contents, 01h discard contents)
   EDX = number of pages to free
   BL = address type
       00h linear address
       ECX = linear address of first page to be freed
       01h pointer
       ES:ECX -> first page to be freed

Return: CF clear if successful
   CF set on error
       EAX = error code
       08h memory error, swap space full, no VMM or DPMI
       09h invalid address