powerpc/pseries: Allow firmware features to match partial strings

This allows firmware_features_table names to add a '*' at the end so that only
partial strings are matched.

When a '*' is added, only upto the '*' is matched when setting firmware feature
bits.

This is useful for the matching best energy feature.

Signed-off-by: Michael Neuling <mikey@neuling.org>
cc: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
cc: Linux PPC dev <linuxppc-dev@ozlabs.org>
Reviewed-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>