base: Make read-only functions const in ScalarBase
base: Make read-only functions const in ScalarBase

These functions do not need to modify their storage's contents.

ScalarBase's non-const value() has been removed.

Change-Id: I4dd3899a29a741a7d8cd199ccd254b346d86ae07
Signed-off-by: Daniel R. Carvalho <91779fc734d358d9575ec4910de29bfcbcaf1b22@yahoo.com.br>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/27084
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>
Maintainer: Bobby R. Bruce <b9dba908ffb6c6d8ffe449cc88b3709c13c485c2@ucdavis.edu>

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