riscv: Add EFI application infrastructure

The hello world binary and a few selftests require to build EFI target
binaries, not just the EFI host environment.

This patch adds all required files to generate an EFI binary for
RISC-V.

Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/arch/riscv/config.mk b/arch/riscv/config.mk
index f65ed87..219e666 100644
--- a/arch/riscv/config.mk
+++ b/arch/riscv/config.mk
@@ -19,10 +19,12 @@
 
 ifdef CONFIG_32BIT
 PLATFORM_LDFLAGS	+= -m $(32bit-emul)
+EFI_LDS			:= elf_riscv32_efi.lds
 endif
 
 ifdef CONFIG_64BIT
 PLATFORM_LDFLAGS	+= -m $(64bit-emul)
+EFI_LDS			:= elf_riscv64_efi.lds
 endif
 
 CONFIG_STANDALONE_LOAD_ADDR = 0x00000000 \
@@ -31,3 +33,6 @@
 PLATFORM_CPPFLAGS	+= -ffixed-gp -fpic
 PLATFORM_RELFLAGS += -fno-strict-aliasing -fno-common -gdwarf-2 -ffunction-sections
 LDFLAGS_u-boot += --gc-sections -static -pie
+
+EFI_CRT0		:= crt0_riscv_efi.o
+EFI_RELOC		:= reloc_riscv_efi.o