Support hardware SHA-256 and SHA-1 on Arm platforms.

Similarly to my recent addition of NEON-accelerated AES, these new
implementations drop in alongside the SHA-NI ones, under a different
set of ifdefs. All the details of selection and detection are
essentially the same as they were for the AES code.

unix/uxutils.c

@@ -16,6 +16,28 @@ bool platform_aes_hw_available(void)
 #endif
 }
 
+bool platform_sha256_hw_available(void)
+{
+#if defined HWCAP_SHA2
+    return getauxval(AT_HWCAP) & HWCAP_SHA2;
+#elif defined HWCAP2_SHA2
+    return getauxval(AT_HWCAP2) & HWCAP2_SHA2;
+#else
+    return false;
+#endif
+}
+
+bool platform_sha1_hw_available(void)
+{
+#if defined HWCAP_SHA1
+    return getauxval(AT_HWCAP) & HWCAP_SHA1;
+#elif defined HWCAP2_SHA1
+    return getauxval(AT_HWCAP2) & HWCAP2_SHA1;
+#else
+    return false;
+#endif
+}
+
 #else
 
 bool platform_aes_hw_available(void)
@@ -23,4 +45,14 @@ bool platform_aes_hw_available(void)
     return false;
 }
 
+bool platform_sha256_hw_available(void)
+{
+    return false;
+}
+
+bool platform_sha1_hw_available(void)
+{
+    return false;
+}
+
 #endif