flushregs is deprecated.

change warning check in RepeatReadTest

debug: Don't rely on RISCV env

Fix for test program compilation failures due to lack of `zicsr` extension in `-march=rvXX...`

That made sense when mostly people used riscv-tools, but now they get
tools from all sorts of places and most of them are suitable for the
debug tests.

Also document RISCV_TESTS_DEBUG_GCC and RISCV_TESTS_DEBUG_GDB
environment variables in the README.

The github workflows that rely on these tests don't use the Makefile,
but instead invoke gdbserver.py directly, so they're not affected by
this change.

Fixes #481

debug: pylint fix.

Github workflow to run pylint against debug tests

Add --target-timeout to debug test script.

I'm using this to greatly reduce the timeout when I'm reproducing a
failure I know is going to time out.

debug: optimize the FreeRtosTest case.

Add a way to exclude tests by specifying an exclusion file

This patch adds a way to specify a yaml file which specifies either
for each target individually or for all targets to exclude tests.
Example file format is included in excluded.yaml.example.

To make sure the rtos module of OpenOCD works well.

Signed-off-by: Chao Du <duchao@eswincomputing.com>

Get gcc and gdb path from environment.

If the environment variables aren't set, then use the same defaults as
previously.

My current set of tools use riscv64-elf-gcc and riscv64-elf-gdb, and
this makes it trivial to use them.

debug: New pylint => new warnings => new cleanups

- Replace general "Exception" with "GdbServerError" in gdbserver.py for when no
samples are collected
- Replace general "Exception" with "TargetsException" in targets.py for XLEN
mismatch
- Introduce "TestLibError" exception in testlib.py and replace general
exceptions in various locations
- Update pylint.rc to remove overgeneral-exceptions warning

New pylint, so make everything clean again.

Update OpenOCD cfg files to new syntax

We were using a variety of deprecated commands.

The driving force behind this was the new way to use `expr{}` as the old
way no longer works with mainline OpenOCD.

Include Zicntr in Spike ISA string

Add more tests for amo[max/maxu/min/minu]_w

Spike no longer enables Zicntr by default, so turn it on explicitly.

cc @jerryz123