PPC32 SHA-256 ASM: small code implementation

Slower but smaller SHA-256 assembly code implementation enabled with:
WOLFSSL_PPC32_ASM_SMALL. (--enable-ppc32=small or
--enable-ppc32=inline,small)

Author: SparkiDev

configure.ac

@@ -3520,8 +3520,11 @@ then
       inline)
         ENABLED_PPC32_ASM_INLINE=yes
         ;;
+      small)
+        ENABLED_PPC32_ASM_SMALL=yes
+        ;;
       *)
-        AC_MSG_ERROR([Invalid RISC-V option [yes,inline]: $ENABLED_PPC32_ASM.])
+        AC_MSG_ERROR([Invalid RISC-V option [yes,inline,small]: $ENABLED_PPC32_ASM.])
         break
         ;;
       esac
@@ -3536,6 +3539,10 @@ if test "$ENABLED_PPC32_ASM_INLINE" = "yes"; then
 else
     AM_CCASFLAGS="$AM_CCASFLAGS -DWOLFSSL_PPC32_ASM"
 fi
+if test "$ENABLED_PPC32_ASM_SMALL" = "yes"; then
+    AM_CFLAGS="$AM_CFLAGS -DWOLFSSL_PPC32_ASM_SMALL"
+    AM_CCASFLAGS="$AM_CCASFLAGS -DWOLFSSL_PPC32_ASM_SMALL"
+fi
 
 # Xilinx hardened crypto
 AC_ARG_ENABLE([xilinx],