ARM: Introduce function to switch to hypervisor mode

On some of the SoCs one cannot enable hypervisor mode directly from the
u-boot because the ROM code puts the chip to supervisor mode after it
jumps to boot loader. Hence introduce a weak function which can be
overridden based on the SoC type and switch to hypervisor mode in a
custom way.

Cc: beagleboard-x15@googlegroups.com
Signed-off-by: Keerthy <j-keerthy@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>

arch/arm/include/asm/system.h

@@ -223,6 +223,10 @@ void __noreturn psci_system_reset(bool smc);
  */
 void save_boot_params_ret(void);
 
+#ifdef CONFIG_ARMV7_LPAE
+void switch_to_hypervisor_ret(void);
+#endif
+
 #define nop() __asm__ __volatile__("mov\tr0,r0\t@ nop\n\t");
 
 #ifdef __ARM_ARCH_7A__