efi_loader: Enable RISC-V support

We have almost all pieces needed to support RISC-V UEFI binaries in place already.
The only missing piece are ELF relocations for runtime code and
data.

This patch adds respective support in the linker script and the runtime
relocation code. It also allows users to enable the EFI_LOADER configuration
switch on RISC-V platforms.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index d532c9f..1a1ca60 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -228,7 +228,7 @@
 
 config CMD_BOOTEFI_HELLO_COMPILE
 	bool "Compile a standard EFI hello world binary for testing"
-	depends on CMD_BOOTEFI && (ARM || X86)
+	depends on CMD_BOOTEFI && (ARM || X86 || RISCV)
 	default y
 	help
 	  This compiles a standard EFI hello world application with U-Boot so