[General] Add new builtin types to support capabilities

[General] Add new builtin types to support capabilities

This patch adds some required builtin types so GDB can properly support
capabilities.

We need a data capability and a code capability. Those are not expected to
yield valid conversions between themselves.

gdb/ChangeLog

2020-10-20  Luis Machado  <luis.machado@arm.com>

	* gdbtypes.h (enum type_code) <TYPE_CODE_CAPABILITY>: New enum.
	(struct builtin_type) <builtin_data_addr_capability>
	<builtin_code_addr_capability>: New fields.