efi_loader: Enable RISCV_EFI_BOOT_PROTOCOL support

This adds support for new RISCV_EFI_BOOT_PROTOCOL to
communicate the boot hart ID to bootloader/kernel on RISC-V
UEFI platforms.

The specification of the protocol is hosted at:
https://github.com/riscv-non-isa/riscv-uefi

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>

include/efi_riscv.h

@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * RISCV_EFI_BOOT_PROTOCOL
+ *
+ * Copyright (c) 2022 Ventana Micro Systems Inc
+ */
+
+#include <efi_api.h>
+
+#define RISCV_EFI_BOOT_PROTOCOL_REVISION 0x00010000
+
+/**
+ * struct riscv_efi_boot_protocol - RISCV_EFI_BOOT_PROTOCOL
+ * @revision:		Version of the protocol implemented
+ * @get_boot_hartid:	Get the boot hart ID
+ */
+struct riscv_efi_boot_protocol {
+	u64 revision;
+
+	efi_status_t (EFIAPI * get_boot_hartid) (struct riscv_efi_boot_protocol *this,
+						 efi_uintn_t *boot_hartid);
+};
+
+extern struct riscv_efi_boot_protocol riscv_efi_boot_prot;