sim-se: Implement fchmodat syscall
sim-se: Implement fchmodat syscall

Signed-off-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Change-Id: Id3b738fa50d0739da5df856c87a8e172ec7a423a
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/51747
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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