gdb: add default description reg types

gdb: add default description reg types

Add support for the default gdb register description type "int" and "float".
When this is given to gdb it will use the bitsize to determine the reg size.

Change-Id: Iaeed594d1feece54044128eae1baff9858bdcae0
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/1622
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>