arm: Add command-line option for enabling CVE-2021-35465 mitigation [PR102035]

arm: Add command-line option for enabling CVE-2021-35465 mitigation [PR102035]

Add a new option, -mfix-cmse-cve-2021-35465 and document it.  Enable it
automatically for cortex-m33, cortex-m35p and cortex-m55.

gcc:
	PR target/102035
	* config/arm/arm.opt (mfix-cmse-cve-2021-35465): New option.
	* doc/invoke.texi (Arm Options): Document it.
	* config/arm/arm-cpus.in (quirk_vlldm): New feature bit.
	(ALL_QUIRKS): Add quirk_vlldm.
	(cortex-m33): Add quirk_vlldm.
	(cortex-m35p, cortex-m55): Likewise.
	* config/arm/arm.c (arm_option_override): Enable fix_vlldm if
	targetting an affected CPU and not explicitly controlled on
	the command line.