Int 2F Fn 4A02  - DOS 5+ - Allocate Hma Space                              [D]

   AX = 4A02h
   BX = number of bytes

Return: ES:DI -> start of allocated HMA block or FFFFh:FFFFh
   BX = number of bytes actually allocated (rounded up to next paragraph
       for DOS 5.0 and 6.0)

Notes: this call is not valid unless DOS is loaded in the HMA (DOS=HIGH)
   called by Windows 3.1 DOSX.EXE

See Also: AX=4A01h