BootLinuxConsoleTest: Test the RX GDB simulator

BootLinuxConsoleTest: Test the RX GDB simulator

Add two tests for the rx-gdbsim machine, based on the recommended
test setup from Yoshinori Sato:
https://lists.gnu.org/archive/html/qemu-devel/2019-05/msg03586.html

- U-Boot prompt
- Linux kernel with Sash shell

These are very quick tests:

  $ avocado run -t arch:rx tests/acceptance/machine_rx_gdbsim.py
  JOB ID     : 84a6ef01c0b87975ecbfcb31a920afd735753ace
  JOB LOG    : /home/phil/avocado/job-results/job-2019-05-24T05.02-84a6ef0/job.log
   (1/2) tests/acceptance/machine_rx_gdbsim.py:RxGdbSimMachine.test_uboot: PASS (0.11 s)
   (2/2) tests/acceptance/machine_rx_gdbsim.py:RxGdbSimMachine.test_linux_sash: PASS (0.45 s)
  RESULTS    : PASS 2 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 0 | CANCEL 0

Tests can also be run with:

  $ avocado --show=console run -t arch:rx tests/acceptance/machine_rx_gdbsim.py
  console: U-Boot 2016.05-rc3-23705-ga1ef3c71cb-dirty (Feb 05 2019 - 21:56:06 +0900)
  console: Linux version 4.19.0+ (yo-satoh@yo-satoh-debian) (gcc version 9.0.0 20181105 (experimental) (GCC)) #137 Wed Feb 20 23:20:02 JST 2019
  console: Built 1 zonelists, mobility grouping on.  Total pages: 8128
  ...
  console: SuperH (H)SCI(F) driver initialized
  console: 88240.serial: ttySC0 at MMIO 0x88240 (irq = 215, base_baud = 0) is a sci
  console: console [ttySC0] enabled
  console: 88248.serial: ttySC1 at MMIO 0x88248 (irq = 219, base_baud = 0) is a sci

Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Signed-off-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Message-Id: <20200224141923.82118-22-ysato@users.sourceforge.jp>
[PMD: Replace obsolete set_machine() by machine tag, and rename as gdbsim]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>