[sw/spiflash] Remove OpenSSL dep. from spiflash

Switch spiflash to use the SHA256 implementation provided by
the vendored in cryptoc library.

Signed-off-by: Miguel Osorio <miguelosorio@google.com>
diff --git a/sw/vendor/meson.build b/sw/vendor/meson.build
index 6c1290a..8b9e7fb 100644
--- a/sw/vendor/meson.build
+++ b/sw/vendor/meson.build
@@ -10,6 +10,16 @@
   'eembc_coremark/core_util.c',
 ])
 
+vendor_cryptoc_sha256 = declare_dependency(
+  include_directories: include_directories(
+    'cryptoc/include',
+    is_system: true,
+  ),
+  sources: [
+    'cryptoc/sha256.c',
+  ],
+)
+
 # googletest and googlemock build definitions
 #
 # The following is inspired by the meson configuration available in