[PATCH, GCC/ARM] Fix MVE scalar shift tests

[PATCH, GCC/ARM] Fix MVE scalar shift tests

*** gcc/ChangeLog ***

2020-02-21  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>

	* config/arm/arm.md: Prevent scalar shifts from being
	used when big endian is enabled.

*** gcc/testsuite/ChangeLog ***

2020-02-21  Mihail-Calin Ionescu  <mihail.ionescu@arm.com>

	* gcc.target/arm/armv8_1m-shift-imm-1.c: Add MVE target checks.
	* gcc.target/arm/armv8_1m-shift-reg-1.c: Likewise.
	* lib/target-supports.exp
	(check_effective_target_arm_v8_1m_mve_ok_nocache): New.
	(check_effective_target_arm_v8_1m_mve_ok): New.
	(add_options_for_v8_1m_mve): New.