arm64: pmap: Mask VA operand in TLBI instructions

Bits 43:0 of the TLBI operand are bits 55:12 of the VA. Leaving
bits 63:55 of the VA in bits 51:44 of the operand might wind up
setting the TTL field (47:44) and accidentally restricting which
translation levels are flushed in the TLB.

Reviewed By: andrew
MFC after: 3 days
Sponsored by: Ampere Computing
Differential Revision: https://reviews.freebsd.org/D34664