lib: sbi_trap: Set hstatus.GVA when going to HS-mode

The privileged spec specifies that on a trap to HS-mode, hstatus.GVA
should be set to 1 if stval is written with a guest virtual address, and
to 0 otherwise. Implement this by setting hstatus.GVA to trap->gva when
redirecting traps to HS-mode.

Signed-off-by: Vivian Wang <dramforever@live.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Anup Patel <anup@brainfault.org>