cmake: Fix ArmClang generated images

Images generated for cortex-m7 targets are not booting.
This is because hardware floating point initialization modules
are added by ArmClang linker. These modules add floating point
instructions that cause exceptions.

This patch adds the linker option to omit including the floating
point initialization modules and the compiler option to avoid
using floating point instructions.

Signed-off-by: Ahmed Gadallah <ahmed.gadallah@arm.com>
Change-Id: I7e0f868227587c0a167d29974608ddb2a21b018f