[ARM] arm32ve: Fix HTCR_T0SZ_MASK define

The T0SZ field of HTCR register is 3bits wide and not 2bits wides
hence this patch fixes the related field mask.

With this patch we have Xvisor ARM32ve booting reliably on Cubieboard2.

Signed-off-by: Anup Patel <anup@brainfault.org>