Make "end" field in feature specs required again.

Make "end" field in feature specs required again.

Newer gdbservers may be talking to older gdbs,
and older gdbs will flag a missing "end" as an error.
So just make "end" required again, and for compatibility
change the default field type to "bool".

gdb/ChangeLog:

	* features/aarch64-core.xml (cpsr_flags): Elide "type" and specify
	"end" in all fields.
	* features/aarch64.c: Regenerate.
	* features/i386/32bit-mpx.xml (_bndcfgu): Specify type of "preserved"
	and "enabled" fields. Correct size of "enabled" field.
	* features/i386/64bit-mpx.xml (_bndcfgu): Specify type of "preserved"
	and "enabled" fields.
	* features/i386/i386-avx-mpx-linux.c: Regenerate.
	* features/i386/i386-avx-mpx.c: Regenerate.
	* features/i386/i386-avx512-linux.c: Regenerate.
	* features/i386/i386-avx512.c: Regenerate.
	* features/i386/i386-mpx-linux.c: Regenerate.
	* features/i386/i386-mpx.c: Regenerate.
	* xml-tdesc.c (tdesc_start_field): Require "end" spec.  Single bit
	fields default to "bool" type.

	Revert 2016-03-15  Doug Evans  <dje@google.com>
	* features/i386/32bit-core.xml (i386_eflags): Remove "end" spec.
	* features/i386/32bit-sse.xml (i386_eflags): Ditto.
	* features/i386/64bit-core.xml (i386_eflags): Ditto.
	* features/i386/64bit-sse.xml (i386_eflags): Ditto.
	* features/i386/x32-core.xml (i386_eflags): Ditto.

gdb/doc/ChangeLog:

	* gdb.texinfo (Target Description Format): Update docs on "end"
	field spec and field default type.

gdb/testsuite/ChangeLog:

	* gdb.xml/extra-regs.xml: Update, end field now required, default type
	for single bitfields is bool.
	* gdb.xml/tdesc-regs.exp: Ditto.