hw/arm/boot: Set NSACR.{CP11, CP10} in dummy SMC setup routine

hw/arm/boot: Set NSACR.{CP11, CP10} in dummy SMC setup routine

The boot.c code usually puts the CPU into NS mode directly when it is
booting a kernel.  Since fc1120a7f5f2d4b6 this has included a
requirement to set NSACR to give NS state access to the FPU; we fixed
that for the usual code path in ece628fcf6.  However, it is also
possible for a board model to request an alternative mode of booting,
where its 'board_setup' code hook runs in Secure state and is
responsible for doing the S->NS transition after it has done whatever
work it must do in Secure state.  In this situation the board_setup
code now also needs to update NSACR.

This affects all boards which set info->secure_board_setup, which is
currently the 'raspi' and 'highbank' families.  They both use the
common arm_write_secure_board_setup_dummy_smc().

Set the NSACR CP11 and CP10 bits in the code written by that
function, to allow FPU access in Non-Secure state when using dummy
SMC setup routine.  Otherwise an AArch32 kernel booted on the
highbank or raspi boards will UNDEF as soon as it tries to use the
FPU.

Update the comment describing secure_board_setup to note the new
requirements on users of it.

This fixes a kernel panic when booting raspbian on raspi2.

Successfully tested with:
  2017-01-11-raspbian-jessie-lite.img
  2018-11-13-raspbian-stretch-lite.img
  2019-07-10-raspbian-buster-lite.img

Fixes: fc1120a7f5
Signed-off-by: Clement Deschamps <clement.deschamps@greensocs.com>
Tested-by: Laurent Bonnans <laurent.bonnans@here.com>
Message-id: 20191104151137.81931-1-clement.deschamps@greensocs.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
[PMM: updated comment to boot.h to note new requirement on
 users of secure_board_setup; edited/rewrote commit message]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>