Ran into this while looking at some new crypto code using FPU
hitting a WARN_ON_ONCE(!irq_fpu_usable()) in the kernel_fpu_begin()
on a x86 kernel that uses the new eagerfpu model. In short, current eagerfpu
changes return 0 for interrupted_kernel_fpu_idle() and the in_interrupt()
thinks it is in the interrupt context because of the local_bh_disable().
Thus resulting in the WARN_ON().

Remove the local_bh_disable/enable() calls around the existing
local_irq_disable/enable() calls. local_irq_disable/enable() already
disables the BH.

 [ If there are any other legitimate users calling kernel_fpu_begin() from
   the process context but with BH disabled, then we can look into fixing the
   irq_fpu_usable() in future. ]
Signed-off-by: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>