added imulu_b lmulu_b and smulu_b

[ZERICO2005]

Added some CRT routines (along with _fast variants) for 32/24/16bit * 8bit unsigned multiplication.
imulu_b: UHL = UHL * A (same as Zilog's/Ti's imul_b)
smulu_b: HL = HL * A
lmulu_b: EUHL = EUHL * A

lmulu_b copies the calling convention of ladd_b. Not quite sure what calling convention would be used for i48mulu_b.

smulu       : 20*r(PC) +  6*r(SPL) +  3*w(SPL) + 13
smulu_b     : 15*r(PC) +  6*r(SPL) +  3*w(SPL) +  9

imulu       : 49*r(PC) + 15*r(SPL) + 12*w(SPL) + 25
imulu_b     : 32*r(PC) + 12*r(SPL) +  9*w(SPL) + 13

lmulu       : 93*r(PC) + 15*r(SPL) + 15*w(SPL) + 41
lmulu_b     : 43*r(PC) + 12*r(SPL) +  9*w(SPL) + 13