tfm: interface: Fix bug where FPU registers were not restored correctly
tfm: interface: Fix bug where FPU registers were not restored correctly

The caller saved registers were restored both as caller saved and
callee saved registers, i.e. register 0-15 were restored into
both register 0-15 and 15-31.

Signed-off-by: Øyvind Rønningstad <5f9e1eedbdafebd99226f1498f634e1047455d88@nordicsemi.no>

zephyrproject-rtos/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,galak/zephyr,finikorg/zephyr,finikorg/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,zephyrproject-rtos/zephyr,galak/zephyr,finikorg/zephyr