aarch64: Generalise TFmode load/store pair patterns

aarch64: Generalise TFmode load/store pair patterns

This patch generalises the TFmode load/store pair patterns to TImode and
TDmode.  This brings them in line with the DXmode patterns, and uses the
same technique with separate mode iterators (TX and TX2) to allow for
distinct modes in each arm of the load/store pair.

For example, in combination with the post-RA load/store pair fusion pass
in the following patch, this improves the codegen for the following
varargs testcase involving TImode stores:

void g(void *);
int foo(int x, ...)
{
    __builtin_va_list ap;
    __builtin_va_start (ap, x);
    g(&ap);
    __builtin_va_end (ap);
}

from:

foo:
.LFB0:
	stp	x29, x30, [sp, -240]!
.LCFI0:
	mov	w9, -56
	mov	w8, -128
	mov	x29, sp
	add	x10, sp, 176
	stp	x1, x2, [sp, 184]
	add	x1, sp, 240
	add	x0, sp, 16
	stp	x1, x1, [sp, 16]
	str	x10, [sp, 32]
	stp	w9, w8, [sp, 40]
	str	q0, [sp, 48]
	str	q1, [sp, 64]
	str	q2, [sp, 80]
	str	q3, [sp, 96]
	str	q4, [sp, 112]
	str	q5, [sp, 128]
	str	q6, [sp, 144]
	str	q7, [sp, 160]
	stp	x3, x4, [sp, 200]
	stp	x5, x6, [sp, 216]
	str	x7, [sp, 232]
	bl	g
	ldp	x29, x30, [sp], 240
.LCFI1:
	ret

to:

foo:
.LFB0:
	stp	x29, x30, [sp, -240]!
.LCFI0:
	mov	w9, -56
	mov	w8, -128
	mov	x29, sp
	add	x10, sp, 176
	stp	x1, x2, [sp, 1bd4971b7c71e70a637a1dq84]
	add	x1, sp, 240
	add	x0, sp, 16
	stp	x1, x1, [sp, 16]
	str	x10, [sp, 32]
	stp	w9, w8, [sp, 40]
	stp	q0, q1, [sp, 48]
	stp	q2, q3, [sp, 80]
	stp	q4, q5, [sp, 112]
	stp	q6, q7, [sp, 144]
	stp	x3, x4, [sp, 200]
	stp	x5, x6, [sp, 216]
	str	x7, [sp, 232]
	bl	g
	ldp	x29, x30, [sp], 240
.LCFI1:
	ret

Note that this patch isn't neeed if we only use the mode
canonicalization approach in the new ldp fusion pass (since we
canonicalize T{I,F,D}mode to V16QImode), but we seem to get slightly
better performance with mode canonicalization disabled (see
--param=aarch64-ldp-canonicalize-modes in the following patch).

gcc/ChangeLog:

	* config/aarch64/aarch64.md (load_pair_dw_tftf): Rename to ...
	(load_pair_dw_<TX:mode><TX2:mode>): ... this.
	(store_pair_dw_tftf): Rename to ...
	(store_pair_dw_<TX:mode><TX2:mode>): ... this.
	* config/aarch64/iterators.md (TX2): New.