bignum: refactored the hardware abstraction of the mpi peripheral

- `<target>/bignum.c` is replaced by mpi_ll.h ll layer.
- added the mpi hal layer.

components/soc/esp32c6/mpi_periph.c

@@ -0,0 +1,21 @@
+/*
+ * SPDX-FileCopyrightText: 2023 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "soc/rsa_reg.h"
+#include "soc/mpi_periph.h"
+
+const uint32_t MPI_LL_BLOCK_BASES[4] = {
+    RSA_X_MEM,
+    RSA_Y_MEM,
+    RSA_Z_MEM,
+    RSA_M_MEM,
+};
+
+const uint32_t MPI_LL_OPERATIONS[3] = {
+    RSA_SET_START_MULT_REG,
+    RSA_SET_START_MODMULT_REG,
+    RSA_SET_START_MODEXP_REG,
+};