FPU save/restore support

# Intro

These commits added support of FPU register value save/restore when switching threads for [Composite OS](https://github.com/gparmer/Composite)

# Changed File List

### Kernel

##### Implementation

src/kernel/include/fpu.h

src/kernel/fpu.c

##### Added FPU structure to thread structure

src/kernel/include/thread.h

src/kernel/thread.c

##### Added fpu_save & fpu_restore to thread switching

src/kernel/inv.c

src/kernel/include/shared/cos_config.h

### Component

##### Component used to test functions

src/components/implementation/no_interface/fpu/f.c

src/components/implementation/no_interface/fpu/Makefile  

src/platform/linux/util/Makefile.end

src/platform/linux/util/lfpu.sh

### Hijack

##### Added code to intercept FPU exception

src/platform/linux/module/hw_ints.c

src/platform/linux/module/kern_entry.S

##### Added fpu_save & fpu_restore exception handling

src/platform/linux/module/hijack.c

src/platform/linux/module/Makefile