mem: Add external TLBI flags to the Request object
mem: Add external TLBI flags to the Request object

* TLBI_EXT_SYNC: This flag tells the CPU model that a
remote TLBI Sync has been requested

* TLBI_EXT_SYNC_COMP: This flag tells the interconnect that a
remote TLBI Sync request has completed

JIRA: https://gem5.atlassian.net/browse/GEM5-1097

Change-Id: I459d22f112038cc1427e24999904ba74c1c08cfb
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/57289
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Reviewed-by: Andreas Sandberg <c9f5686ee5bd561c93f9de79681eee75bfa7f36e@arm.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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