hw/arm/boot: Set SCR_EL3.FGTEn when booting kernel

Just like d7ef5e1 sets SCR_EL3.HXEn for FEAT_HCX, this commit
handles SCR_EL3.FGTEn for FEAT_FGT:

When we direct boot a kernel on a CPU which emulates EL3, we need to
set up the EL3 system registers as the Linux kernel documentation
specifies:
    https://www.kernel.org/doc/Documentation/arm64/booting.rst

> For CPUs with the Fine Grained Traps (FEAT_FGT) extension present:
> - If EL3 is present and the kernel is entered at EL2:
>   - SCR_EL3.FGTEn (bit 27) must be initialised to 0b1.

Cc: qemu-stable@nongnu.org
Signed-off-by: Fabian Vogt <fvogt@suse.de>
Message-id: 4831384.GXAFRqVoOG@linux-e202.suse.de
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/arm/boot.c

@@ -761,6 +761,10 @@ static void do_cpu_reset(void *opaque)
                     if (cpu_isar_feature(aa64_hcx, cpu)) {
                         env->cp15.scr_el3 |= SCR_HXEN;
                     }
+                    if (cpu_isar_feature(aa64_fgt, cpu)) {
+                        env->cp15.scr_el3 |= SCR_FGTEN;
+                    }
+
                     /* AArch64 kernels never boot in secure mode */
                     assert(!info->secure_boot);
                     /* This hook is only supported for AArch32 currently: