mpfs_mm_init.c: Ensure the L3 page table size is large enough

Run-time check for L3 page table size, to ensure it is large enough
to map all of the kernel memory.

NOTE: The check has to be run-time, as KFLASH_SIZE/KSRAM_SIZE are really
linker relocation symbols, and thus cannot be utilized compile-time.

arch/risc-v/src/mpfs/mpfs_mm_init.c

@@ -58,6 +58,11 @@
 #define PGT_L2_SIZE     (512)  /* Enough to map 1 GiB */
 #define PGT_L3_SIZE     (1024) /* Enough to map 4 MiB */
 
+/* Calculate the minimum size for the L3 table */
+
+#define KMEM_SIZE       (KFLASH_SIZE + KSRAM_SIZE)
+#define PGT_L3_MIN_SIZE ((KMEM_SIZE + RV_MMU_PAGE_MASK) >> RV_MMU_PAGE_SHIFT)
+
 #define SLAB_COUNT      (sizeof(m_l3_pgtable) / RV_MMU_PAGE_SIZE)
 
 /****************************************************************************
@@ -214,6 +219,10 @@ void mpfs_kernel_mappings(void)
   ASSERT((KSRAM_START & RV_MMU_SECTION_ALIGN) == 0);
   ASSERT((PGPOOL_START & RV_MMU_SECTION_ALIGN) == 0);
 
+  /* Check that the L3 table is of sufficient size */
+
+  ASSERT(PGT_L3_SIZE >= PGT_L3_MIN_SIZE);
+
   /* Initialize slab allocator for L3 page tables */
 
   slab_init(PGT_L3_PBASE);