arm64/vmm: Support tlbi from VHE

When invalidating the stage 2 TLB we need to ensure page tables updates
have completed and for tlbi vmalle1is the HCR_EL2 TGE flag needs to be
clear.

To fix the former add a data barrier before the tlbi instructions. On
non-VHE this will happen as part of the exception entry, so is only
needed for VHE.

The tlbi vmalle1is instruction operates on the EL2 & 0 regime when
HCR_EL2 E2H and TGE flags are both set. By clearing the TGE flag it
will stop this and operate on the EL1 & 0 regime we are expecting.

Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D46080