base: Use M5_UNLIKELY for conditional panic, etc., macros.
base: Use M5_UNLIKELY for conditional panic, etc., macros.

panic_if and fail_if should happen at most once in any given simulation,
and warn_if, etc., should still not happen most of the time.

Change-Id: Iaa6cb03c11b86d84f51cc4738efb8f203de4201c
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/34817
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5,gem5/gem5