base: Using scoped string in DPRINTFNR
base: Using scoped string in DPRINTFNR

We would otherwise need to add a using namespace std wherever we
use DPRINTFNR.

Change-Id: I30bf9ba474408133abded66141f6dc96dfdba8d6
Signed-off-by: Giacomo Travaglini <8eef13a4f970e2e9372c8d26ad0737b760f99c02@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/21821
Reviewed-by: Jason Lowe-Power <68c46a606457643eab92053c1c05574abb26f861@lowepower.com>
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Jason Lowe-Power <68c46a606457643eab92053c1c05574abb26f861@lowepower.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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