[gdb/testsuite] Fix TUI tests on freebsd

[gdb/testsuite] Fix TUI tests on freebsd

While re-testing the TUI tests on x86_64-freebsd, I found that commit
06a53717f7c ("[gdb/testsuite] Handle unrecognized escape sequences better in
tuiterm") broke most test-cases.

Fix this by rewriting this gdb_test_multiple clause:
...
 	-re "^($re_csi_prefix?)($re_csi_args*)($re_csi_cmd)" {
...
into:
...
	-re "^($re_csi_cmd)" {
  ...
	-re "^($re_csi_args*)($re_csi_cmd)" {
  ...
 	-re "^($re_csi_prefix?)($re_csi_args*)($re_csi_cmd)" {
...

Tested on x86_64-linux and x86_64-freebsd.