Fixed __ldvrmu calling convention and __ldiv (#793)

[ZERICO2005]

Fixes #793

I also made it so __ldvrmu follows Zilog's calling conventions, with the exx __ldvrmu routine being renamed to __ldivu_lremu_common since it uses a completely different calling convention.

Zilog __ldvrmu:
; I: EUHL=dividend, AUBC=divisor
; O: a[uhl']=EUHL%AUBC, bcu=0, b=A, c=?, euhl=EUHL/AUBC, eubc'=AUBC, zf=!IEF2

exx __ldvrmu:
; I: EUHL=dividend, AUBC=divisor
; O: auhl=EUHL%AUBC, euix=EUHL/AUBC, iyh=A, iyl=0