arm: Restrict support of vectors of boolean immediates (PR target/104662)

arm: Restrict support of vectors of boolean immediates (PR target/104662)

This simple patch avoids the ICE described in the PR:
internal compiler error: in simd_valid_immediate, at config/arm/arm.cc:12866

with an early exit from simd_valid_immediate if we are trying to
handle a vector of booleans and MVE is not enabled.

We still get an ICE when compiling the existing
gcc.dg/rtl/arm/mve-vxbi.c without -march=armv8.1-m.main+mve:

error: unrecognizable insn:
(insn 7 5 8 2 (set (reg:V4BI 114)
        (const_vector:V4BI [
                (const_int 1 [0x1])
                (const_int 0 [0]) repeated x2
                (const_int 1 [0x1])
            ])) -1
     (nil))
during RTL pass: ira

but there's little we can do since the testcase explicitly creates
vectors of booleans which do need MVE.

That is the reason why I do not add a testcase.

2022-04-19  Christophe Lyon  <christophe.lyon@arm.com>

	PR target/104662
	* config/arm/arm.cc (simd_valid_immediate): Exit when input is a
	vector of booleans and MVE is not enabled.