efi: add API to reserve memory persistently across kexec reboot

Add kernel plumbing to reserve memory regions persistently on a EFI
system by adding entries to the MEMRESERVE linked list.

Tested-by: Jeremy Linton <jeremy.linton@arm.com>
Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
diff --git a/include/linux/efi.h b/include/linux/efi.h
index a5cb5804..22e4de9 100644
--- a/include/linux/efi.h
+++ b/include/linux/efi.h
@@ -1043,6 +1043,7 @@ extern int __init efi_uart_console_only (void);
 extern u64 efi_mem_desc_end(efi_memory_desc_t *md);
 extern int efi_mem_desc_lookup(u64 phys_addr, efi_memory_desc_t *out_md);
 extern void efi_mem_reserve(phys_addr_t addr, u64 size);
+extern int efi_mem_reserve_persistent(phys_addr_t addr, u64 size);
 extern void efi_initialize_iomem_resources(struct resource *code_resource,
 		struct resource *data_resource, struct resource *bss_resource);
 extern void efi_reserve_boot_services(void);