Add switch to control compact/verbose printing of capabilities

Add switch to control compact/verbose printing of capabilities

Add a new option set/show "print compact-capabilities" that default to "on".

This makes GDB default to printing capabilities in compact format, the CHERI
format.

gdb/ChangeLog:

2020-12-30  Luis Machado  <luis.machado@arm.com>

	* valprint.c (user_print_options): Initialize compact_capabilities.
	(show_print_compact_capabilities): New function.
	(generic_value_print_capability): Use compact_capabilities option.
	(value_print_option_defs): New compact_capabilities option.
	* valprint.h (value_print_options) <compact_capabilities>: New member
	variable.