[VE][NFC] Change to use l2i/i2l to simplify code

We previously added l2i/i2l macros to simpily EXTRACT_SUBREG/INSERT_SUBREG
conversions.  This patch changes VEInstrInfo.td to use such macros to
simplify existing code.

Reviewed By: efocht

Differential Revision: https://reviews.llvm.org/D134118