Add compile option to disable floating point usage (#114)

This commit adds the option to disable floating point processing in
QCBOR. To disable, the USEFULBUF_DISABLE_ALL_FLOAT preprocessor macro
needs to be defined.

e.g.:

 $ make CMD_LINE="-DUSEFULBUF_DISABLE_ALL_FLOAT"

This removes the capability (and the code) of decoding floating point
types. The type is still recognised, so a meaningful
QCBOR_ERR_ALL_FLOAT_DISABLED error is returned when a floating point value
is encountered in a decoded qcbor. From the encoding interface the
floating point encoding functions are removed.

Change-Id: I371769246f7d83354607de9bce1e7998b8c536a1
Signed-off-by: Mate Toth-Pal <mate.toth-pal@arm.com>
diff --git a/src/qcbor_err_to_str.c b/src/qcbor_err_to_str.c
index e96ed70..4879f91 100644
--- a/src/qcbor_err_to_str.c
+++ b/src/qcbor_err_to_str.c
@@ -3,6 +3,7 @@
 
  Copyright (c) 2020, Patrick Uiterwijk. All rights reserved.
  Copyright (c) 2020, Laurence Lundblade.
+ Copyright (c) 2021, Arm Limited. All rights reserved.
 
  SPDX-License-Identifier: BSD-3-Clause
 
@@ -60,6 +61,7 @@
     _ERR_TO_STR(ERR_HALF_PRECISION_DISABLED)
     _ERR_TO_STR(ERR_HW_FLOAT_DISABLED)
     _ERR_TO_STR(ERR_FLOAT_EXCEPTION)
+    _ERR_TO_STR(ERR_ALL_FLOAT_DISABLED)
 
     default:
         return "Unidentified error";