[icp] fpu and asm cleanup for linux

[icp] fpu and asm cleanup for linux

Properly annotate functions and data section so that objtool does not complain
when CONFIG_STACK_VALIDATION and CONFIG_FRAME_POINTER are enabled.

Pass KERNELCPPFLAGS to assembler.

Use kfpu_begin()/kfpu_end() to protect SIMD regions in Linux kernel.

Reviewed-by: Tom Caputi <tcaputi@datto.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Gvozden Neskovic <neskovic@gmail.com>
Closes #5872
Closes #5041