The new spinlock validation features combined with spinlockification
have increased stack usage a bit in CONFIG_ASSERT builds, but this is
a good feature we want to keep. This test was bumping into limits, so
increase the size from 512 to 640 bytes.
Unfortunately, this is also a huge test that creates a LOT of those
stacks across different test cases, so that minor bump blows us past
the 64k SRAM limit on a bunch of boards. So unify all those stacks
that are only ever used in one case at a time so the memory can be
shared. Now there's one fixed stack, named "tstack", and one array
"tstacks". Much smaller.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>