hw/misc/mips_cpc: Start vCPU when powered on

hw/misc/mips_cpc: Start vCPU when powered on

In commit 102ca9667d we set "start-powered-off" on all vCPUs
included in the CPS (Coherent Processing System) but forgot to
start the vCPUS on when they are powered on in the CPC (Cluster
Power Controller).

This fixes the following tests:

  $ avocado run tests/acceptance/machine_mips_malta.py
   (1/3) test_mips_malta_i6400_framebuffer_logo_1core: PASS (3.67 s)
   (2/3) test_mips_malta_i6400_framebuffer_logo_7cores: INTERRUPTED: Test interrupted by SIGTERM (30.22 s)
   (3/3) test_mips_malta_i6400_framebuffer_logo_8cores: INTERRUPTED: Test interrupted by SIGTERM (30.25 s)
  RESULTS    : PASS 1 | ERROR 0 | FAIL 0 | SKIP 0 | WARN 0 | INTERRUPT 2 | CANCEL 0

Fixes: 102ca9667d ("mips/cps: Use start-powered-off CPUState property")
Reported-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20201007113942.2523866-1-f4bug@amsat.org>
Message-Id: <20201007160038.26953-3-alex.bennee@linaro.org>