configure.ac: Tag version 2.3
configure.ac: Tag version 2.3

New features since v2.2:
    - Support for using the SBE to read/write memory
    - General SBE chip-op support
    - Cronus backend
    - Fixed for clang
    - Default device-tree selection for applications
    - Bugfix for newer OpenBMC kernels using alternate FSI paths

Signed-off-by: Alistair Popple <e9adbcf81c8a36ccc628e09bc92d0e25e1c8e501@popple.id.au>

open-power/pdbg,open-power/pdbg,open-power/pdbg