altos: Make ao_xmem funcs require __xdata void * instead of casting

altos: Make ao_xmem funcs require __xdata void * instead of casting

Having an explicit cast in the ao_xmem wrapper macros caused the
compiler to generate garbage values for pdata addresses, making the
upper byte 0x00 instead of the required 0xf0. Removing the
casts from the ao_xmem macros exposed this problem, so a new
PDATA_TO_XDATA macros was added, along with a CODE_TO_XDATA macro
which serve to cast pointers, with suitable address modifications, so
that things work again.

Signed-off-by: Keith Packard <keithp@keithp.com>