arm: Always use vmov.f64 instead of vmov.f32 with MVE

With MVE, vmov.f64 is always supported (no need for +fp.dp extension).

This patch updates two patterns:
- in movdi_vfp, we incorrectly checked
  TARGET_VFP_SINGLE || TARGET_HAVE_MVE instead of
  TARGET_VFP_SINGLE && !TARGET_HAVE_MVE, and didn't take into account
  these two possibilities when computing the length attribute.

- in thumb2_movdf_vfp, we checked only TARGET_VFP_SINGLE.

No need to update movdf_vfp, since it is enabled only for TARGET_ARM
(which is not the case when MVE is enabled).

The patch also updates gcc.target/arm/armv8_1m-fp64-move-1.c, to
accept only vmov.f64 instead of vmov.f32.

Tested on arm-none-eabi with:
qemu/-mthumb/-mtune=cortex-m55/-mfloat-abi=hard/-mfpu=auto
qemu/-mthumb/-mtune=cortex-m55/-mfloat-abi=hard/-mfpu=auto/-march=armv8.1-m.main+mve
qemu/-mthumb/-mtune=cortex-m55/-mfloat-abi=hard/-mfpu=auto/-march=armv8.1-m.main+mve.fp
qemu/-mthumb/-mtune=cortex-m55/-mfloat-abi=hard/-mfpu=auto/-march=armv8.1-m.main+mve.fp+fp.dp

2024-08-21  Christophe Lyon  <christophe.lyon@linaro.org>

	gcc/
	* config/arm/vfp.md (movdi_vfp, thumb2_movdf_vfp): Handle MVE
	case.

	gcc/testsuite/
	* gcc.target/arm/armv8_1m-fp64-move-1.c: Update expected code.