[lldb] Move TestBase.runCmd() to the Base class (#92252)

runCmd() is called from Base.getCPUInfo() but implemented only in
TestBase(Base). Usually it works if TestBase is used. But call
getCPUInfo() from a class based on Base will cause something like
```
File "E:\projects\llvm-nino\lldb\llvm-project\lldb\packages\Python\lldbsuite\test\lldbtest.py", line 1256, in getCPUInfo
  self.runCmd('platform get-file "/proc/cpuinfo" ' + cpuinfo_path)
AttributeError: 'TestGdbRemoteExpeditedRegisters' object has no attribute 'runCmd'
```
BTW, TestBase.setUp() called runCmd() before applying
LLDB_MAX_LAUNCH_COUNT and LLDB_TIME_WAIT_NEXT_LAUNCH.

This patch fixes the test TestGdbRemoteExpeditedRegisters in case of
Windows host and Linux target.