Use relative include paths to support public usage of these headers

fesvr/memif.h

@@ -7,7 +7,7 @@
 #include <stddef.h>
 #include <stdexcept>
 #include "byteorder.h"
-#include "cfg.h"
+#include "../riscv/cfg.h"
 
 typedef uint64_t reg_t;
 typedef int64_t sreg_t;

riscv/decode.h

@@ -7,7 +7,7 @@
 # error spike requires a two''s-complement c++ implementation
 #endif
 
-#include "softfloat_types.h"
+#include "../softfloat/softfloat_types.h"
 #include <algorithm>
 #include <cstdint>
 #include <string.h>

riscv/processor.h

@@ -16,7 +16,7 @@
 #include "csrs.h"
 #include "isa_parser.h"
 #include "triggers.h"
-#include "memif.h"
+#include "../fesvr/memif.h"
 #include "vector_unit.h"
 
 #define N_HPMCOUNTERS 29