UEFI: change the efi_ctx passing method

Save the pointer of efi_ctx in mi_drivers_addr field of
multiboot structure and pass to hypervisor, not by
saving in register RDX(the third default parameter in
64bit call function).

With this method, we can be compatible with the original
32bit boot parameters passing method and no need to
large the array size of boot_regs in hypervisor.

Signed-off-by: Zheng, Gen <gen.zheng@intel.com>

hypervisor/include/arch/x86/multiboot.h

@@ -34,6 +34,7 @@
 #define MULTIBOOT_INFO_MAGIC		    	0x2BADB002
 #define MULTIBOOT_INFO_HAS_CMDLINE		0x00000004
 #define MULTIBOOT_INFO_HAS_MODS			0x00000008
+#define MULTIBOOT_INFO_HAS_DRIVES	0x00000080
 
 struct multiboot_info {
 	uint32_t               mi_flags;