arm: spectre-v2: use arm_smccc_1_1_get_conduit()

arm: spectre-v2: use arm_smccc_1_1_get_conduit()

Now that we have arm_smccc_1_1_get_conduit(), we can hide the PSCI
implementation details from the arm spectre-v2 code, so let's do so.

As arm_smccc_1_1_get_conduit() implicitly checks that the SMCCC version
is at least SMCCC_VERSION_1_1, we no longer need to check this
explicitly where switch statements have a default case.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Russell King <linux@armlinux.org.uk>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>