TLB flush enhancement using hypercall in Hyper-V

[schakrabarti_microsoft.com]

Summary

Currently FreeBSD uses IPI based TLB flushing for remote TLB flushing.
Hyper-V allows hypercalls to flush local and remote TLB. The use of
Hyper-V hypercalls gives significant performance improvement in TLB operations.
This patch set during test has shown near to 40 percent
performance improvement.

Also this patch adds rep hypercall implementation as well.

Authored-by: Souradeep Chakrabarti <[e-mail]>
Co-Authored-by: Erni Sri Satya Vennela <[e-mail]>

Signed-off-by: Souradeep Chakrabarti <[e-mail]>