cc3200/mods/pybpin: Reduce footprint of AF pin structures.

This commit performs a minor change to the "pin_af_t" structure,
changing the data type used to store alternate function pin name QSTRs
in order to have a smaller impact on the .rodata section of the
firmware.

The data type used to store the QSTR name of the pin is changed from
"qstr" to "qstr_short_t", that is able to store the same name string
index but in half the size.

Other pin-related structures in the port that also store QSTRs do not
benefit from a narrower data type, as their members are mostly
word-aligned and thus the linker is forced to insert padding bytes
between entries.

Signed-off-by: Alessandro Gatti <a.gatti@frob.it>

ports/cc3200/mods/pybpin.h

@@ -88,7 +88,7 @@ enum {
 };
 
 typedef struct {
-  qstr name;
+  qstr_short_t name;
   int8_t  idx;
   uint8_t fn;
   uint8_t unit;