hotp: Initial commit for HMAC-OTP (RFC4226)

Add host application and a new TA that are capable of generating HMAC
based One Time Passwords according to the RFC4226 specification [1].

[1] https://www.ietf.org/rfc/rfc4226.txt

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Tested-by: Joakim Bech <joakim.bech@linaro.org> (QEMU v7)
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
diff --git a/hotp/Makefile b/hotp/Makefile
new file mode 100644
index 0000000..3b9a8dc
--- /dev/null
+++ b/hotp/Makefile
@@ -0,0 +1,15 @@
+export V ?= 0
+
+# If _HOST or _TA specific compilers are not specified, then use CROSS_COMPILE
+HOST_CROSS_COMPILE ?= $(CROSS_COMPILE)
+TA_CROSS_COMPILE ?= $(CROSS_COMPILE)
+
+.PHONY: all
+all:
+	$(MAKE) -C host CROSS_COMPILE="$(HOST_CROSS_COMPILE)"
+	$(MAKE) -C ta CROSS_COMPILE="$(TA_CROSS_COMPILE)"
+
+.PHONY: clean
+clean:
+	$(MAKE) -C host clean
+	$(MAKE) -C ta clean