Move Bignum macros to common header

Signed-off-by: Janos Follath <janos.follath@arm.com>
diff --git a/library/bignum_core.h b/library/bignum_core.h
index 847a571..8f48deb 100644
--- a/library/bignum_core.h
+++ b/library/bignum_core.h
@@ -26,6 +26,22 @@
 #include "mbedtls/bignum.h"
 #endif
 
+#define MPI_VALIDATE_RET( cond )                                       \
+    MBEDTLS_INTERNAL_VALIDATE_RET( cond, MBEDTLS_ERR_MPI_BAD_INPUT_DATA )
+#define MPI_VALIDATE( cond )                                           \
+    MBEDTLS_INTERNAL_VALIDATE( cond )
+
+#define ciL    (sizeof(mbedtls_mpi_uint))   /* chars in limb  */
+#define biL    (ciL << 3)                   /* bits  in limb  */
+#define biH    (ciL << 2)                   /* half limb size */
+
+/*
+ * Convert between bits/chars and number of limbs
+ * Divide first in order to avoid potential overflows
+ */
+#define BITS_TO_LIMBS(i)  ( (i) / biL + ( (i) % biL != 0 ) )
+#define CHARS_TO_LIMBS(i) ( (i) / ciL + ( (i) % ciL != 0 ) )
+
 int mbedtls_mpi_core_read_le( mbedtls_mpi_uint *X,
                               size_t nx,
                               const unsigned char *buf,