build: add string casing facilities to utilities

This is a small modification to two existing functions in the build
system: `uppercase` and `lowercase`.

These functions have been moved to the common utilities makefile, and
use the `tr` tool to simplify their implementation. Behaviour is, for
virtually all use-cases, identical.

Change-Id: I0e459d92e454087e4188b2fa5968244e5db89906
Signed-off-by: Chris Kay <chris.kay@arm.com>
3 files changed