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   - Sometimes CPU0 starts before all secondaries are up in vexpress
     increase wait time for all cores
   - Minor README fixes

   - Separate secondary power off functions from system shutdown
   - Put vexpress cores in wfi state when powering down

Pass it properly as a define in the source files.

- CPU idle with wfi, instead of spinning
- Various small changes

For some reason, arm-none-eabi GCC 5.1 does not like the following way
to allocate a static array:
char array[10] = {0};
for an undefined reference of memset().

Changing the linker to gcc might solve the problem, for the time being
workaround the problem initiating the memory manually.

Export the target board type to the C source files, since some
preprocessor conditional code is needed to handle properly the
Vexpress model.

Sample spinlock test case with the option to implement the spinlock
by means of GCC atomic instructions or unsafe memory operations.
Additionally, printf is wrapped around a spinlock to avoid concurrent
access to the serial device.
Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
Signed-off-by: Alexander Spyridakis <a.spyridakis@virtualopensystems.com>

Minimal payload initialization for the virt machine model.
Setup a stack and jump to C code, where CPU0 will boot any
discovered secondary cores through PSCI. Immediately after
all cores are turned-off and the guest is powered down.

Added printf functionality is based on the multiboot test. In a
similar manner this test is standalone and not part of 'make check'.
Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
Signed-off-by: Alexander Spyridakis <a.spyridakis@virtualopensystems.com>