Revert "smcf: Check MODE_STAT after setting MODE_REQ"

The method of application the mode is largely determined by the type of
monitor being used. Each monitor implementation may require different handling.
From a design perspective, it is preferable to delegate this handling to the
specific monitor driver and keep the smcf code generic.

This reverts commit 9860d64b

Signed-off-by: Tarek El-Sherbiny <tarek.el-sherbiny@arm.com>