Update GDB to use new AUXV entry types

I noticed GDB didn't know a particular AT tag (51) when doing some debugging.
Turns out we're missing a few entries compared to glibc's headers.

This patch adds them to GDB and fixes a failure in gdb.base/auxv.exp as
a result.

gdb/ChangeLog:

2020-03-03  Luis Machado  <luis.machado@linaro.org>

	* auxv.c (default_print_auxv_entry): Add new AUXV entries.