aarch64: PR target/102252 Invalid addressing mode for SVE load predicate

aarch64: PR target/102252 Invalid addressing mode for SVE load predicate

In the testcase we generate invalid assembly for an SVE load predicate instruction.
The RTL for the insn is:
(insn 9 8 10 (set (reg:VNx16BI 68 p0)
        (mem:VNx16BI (plus:DI (mult:DI (reg:DI 1 x1 [93])
                    (const_int 8 [0x8]))
                (reg/f:DI 0 x0 [92])) [2 work_3(D)->array[offset_4(D)]+0 S8 A16]))

That addressing mode is not valid for the instruction [1] as it only accepts the addressing mode:
[<Xn|SP>{, #<imm>, MUL VL}]

This patch rejects the register index form for SVE predicate modes.

Bootstrapped and tested on aarch64-none-linux-gnu.

[1] https://developer.arm.com/documentation/ddi0602/2021-06/SVE-Instructions/LDR--predicate---Load-predicate-register-

gcc/ChangeLog:

	PR target/102252
	* config/aarch64/aarch64.c (aarch64_classify_address): Don't allow
	register index for SVE predicate modes.

gcc/testsuite/ChangeLog:

	PR target/102252
	* g++.target/aarch64/sve/pr102252.C: New test.