src/sifive: Add the SiFive Freedom Unleashed 540 SoC

The FU540 is the first RISC-V SoC with the necessary resources to run
Linux (an external memory interface, MMU, etc).

More information is available on SiFive's website:
https://www.sifive.com/products/hifive-unleashed/

Change-Id: Ic2a3c7b1dfa56b67cc0571969cc9cf67a770ae43
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Reviewed-on: https://review.coreboot.org/25789
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>
diff --git a/src/soc/sifive/Kconfig b/src/soc/sifive/Kconfig
new file mode 100644
index 0000000..14900be4
--- /dev/null
+++ b/src/soc/sifive/Kconfig
@@ -0,0 +1,2 @@
+# Load all chipsets
+source "src/soc/sifive/*/Kconfig"