rseq/selftests: Add support for OpenRISC

Add support for OpenRISC in the rseq selftests.  OpenRISC is 32-bit
only.

Tested this with:

    Compiler:  gcc version 14.2.0 (GCC)
    Binutils:  GNU assembler version 2.43.1 (or1k-smh-linux-gnu) using BFD version (GNU Binutils) 2.43.1.20241207
    Linux:     Linux buildroot 6.13.0-rc2-00005-g1fa73dd6c2d3-dirty #213 SMP Sat Dec 28 22:18:39 GMT 2024 openrisc GNU/Linux
    Glibc:     2024-12-13 e4e49583d9 Stafford Horne   or1k: Update libm-test-ulps

Signed-off-by: Stafford Horne <shorne@gmail.com>
Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Acked-by: Shuah Khan <skhan@linuxfoundation.org>