Commit a2cfb8431d ("arch: arm: Add code for swapping threads between
secure and non-secure") changed the mode variable in the _thread_arch to
be defined by ARM_STORE_EXC_RETURN or USERSPACE. The generated offset
define for mode was enabled by FPU_SHARING or USERSPACE. This broke
Cortex-R with FPU, but with ARM_STORE_EXC_RETURN disabled. Reconcile
the checks.
Signed-off-by: Bradley Bolen <bbolen@lexmark.com>