Look in the P18F4455.inc file in your MPASM directory. There's a list of all config options.

New way;
; Single-Supply ICSP Enable bit:
LVP = OFF Single-Supply ICSP disabled
LVP = ON Single-Supply ICSP enabled

Old way;
_LVP_OFF_4L EQU H'FB' ; Single-Supply ICSP disabled
_LVP_ON_4L EQU H'FF' ; Single-Supply ICSP enabled