RISC-V Build Infrastructure

This adds RISC-V into the build system enabling the following targets:

- riscv32-softmmu
- riscv64-softmmu
- riscv32-linux-user
- riscv64-linux-user

This adds defaults configs for RISC-V, enables the build for the RISC-V
CPU core, hardware, and Linux User Emulation. The 'qemu-binfmt-conf.sh'
script is updated to add the RISC-V ELF magic.

Expected checkpatch errors for consistency reasons:

ERROR: line over 90 characters
FILE: scripts/qemu-binfmt-conf.sh

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Sagar Karandikar <sagark@eecs.berkeley.edu>
Signed-off-by: Michael Clark <mjc@sifive.com>

scripts/qemu-binfmt-conf.sh

@@ -4,7 +4,7 @@
 
 qemu_target_list="i386 i486 alpha arm armeb sparc32plus ppc ppc64 ppc64le m68k \
 mips mipsel mipsn32 mipsn32el mips64 mips64el \
-sh4 sh4eb s390x aarch64 aarch64_be hppa"
+sh4 sh4eb s390x aarch64 aarch64_be hppa riscv32 riscv64"
 
 i386_magic='\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\x03\x00'
 i386_mask='\xff\xff\xff\xff\xff\xfe\xfe\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
@@ -100,6 +100,14 @@ hppa_magic='\x7f\x45\x4c\x46\x01\x02\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00
 hppa_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff'
 hppa_family=hppa
 
+riscv32_magic='\x7fELF\x01\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00'
+riscv32_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
+riscv32_family=riscv
+
+riscv64_magic='\x7fELF\x02\x01\x01\x00\x00\x00\x00\x00\x00\x00\x00\x00\x02\x00\xf3\x00'
+riscv64_mask='\xff\xff\xff\xff\xff\xff\xff\x00\xff\xff\xff\xff\xff\xff\xff\xff\xfe\xff\xff\xff'
+riscv64_family=riscv
+
 qemu_get_family() {
     cpu=${HOST_ARCH:-$(uname -m)}
     case "$cpu" in
@@ -124,6 +132,9 @@ qemu_get_family() {
     sparc*)
         echo "sparc"
         ;;
+    riscv*)
+        echo "riscv"
+        ;;
     *)
         echo "$cpu"
         ;;