driver: rng: Do not check ARM_SMCCC_TRNG_VERSION

driver: rng: Do not check ARM_SMCCC_TRNG_VERSION

As described in the document SMC Calling Convention (ARM DEN 0028 1.5 F),
section 7 "Arm Architecture Calls", the SMC call SMCCC_ARCH_FEATURES is
not expected to support the function ID ARM_SMCCC_TRNG_VERSION. Trusted
Firmware-A follows up the specification in its implementation.

This commit removes the invocation to avoid the failure - which is a
wrong calling in U-boot. The later code invokes ARM_SMCCC_TRNG_VERSION
for retrieving the TRNG version, except it can read back the version
number, it also can be used to detect whether the TRNG is supported or
not.

Signed-off-by: Leo Yan <leo.yan@arm.com>
Reviewed-by: Weizhao Ouyang <o451686892@gmail.com>