SP: --enable-sp-asm now enables SP if not set

Enabling SP with ASM didn't enable SP or error out when SP wasn't
configured. Now enables SP when '' and errors when 'no'.

SAKKE modinv used large amounts of stack. Change to have more temporary
memory allocated increased to cover the usage.
ECC, SAKKE: sp_<bits>_ecc_mulmod_<cpu><words>() used large amounts of
stack. Allocate when WOLFSSL_SMALL_STACK.

wc_DhCheckKeyPair() not available when HAVE_SELFTEST.
Wasn't compiled in before as WOLFSSL_HAVE_SP_DH wasn't defined.

Author: SparkiDev

configure.ac

@@ -566,6 +566,17 @@ AC_ARG_ENABLE([sp-asm],
     [ ENABLED_SP_ASM=$SP_ASM_DEFAULT ],
     )
 
+if test "$ENABLED_SP_ASM" != "no"
+then
+    if test "$ENABLED_SP" = "no"
+    then
+        AC_MSG_ERROR([--enable-sp-asm requries SP to be enabled.])
+    fi
+    if test "$ENABLED_SP" = ""
+    then
+        ENABLED_SP=yes
+    fi
+fi
 
 # fastmath
 AC_ARG_ENABLE([fastmath],