TF-M: Bring in option for enabling FPU

Update TF-M to the latest and bring in its new option
`CONFIG_TFM_ENABLE_FPU` which enables the FPU and permits non-secure
access to it.

Note: `CONFIG_TFM_ENABLE_FPU=ON` alone does not cause TF-M to use any
floating point instructions, but this option is necessary if the non-
secure application uses hardware floating point. Without this set, any
non-secure floating point instructions will trigger a Usage Fault.

Signed-off-by: Lingkai Dong <lingkai.dong@arm.com>