powerpc/mce: Reduce the size of event arrays

Maximum recursive depth of MCE is 4, Considering the maximum depth
allowed reduce the size of event to 10 from 100. This saves us ~19kB
of memory and has no fatal consequences.

Signed-off-by: Ganesh Goudar <ganeshgr@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210128104143.70668-1-ganeshgr@linux.ibm.com