[ARM] Allow +nodsp for -mcpu=cortex-m33

DSP instructions are optional for Arm Cortex-M33, yet its -mcpu option
does not allow +nodsp. Users are thus left with using
-march=armv8-m.main -mtune=cortex-m33. This patch allows +nodsp to
-mcpu=cortex-m33.

2017-10-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>

    gcc/
    * config/arm/arm-cpus.in (cortex-m33): Add nodsp option.
    * doc/invoke.texi: Document +nodsp as a valid extension for
    -mcpu=cortex-m33.

From-SVN: r253787

gcc/ChangeLog

+2017-10-16  Thomas Preud'homme  <thomas.preudhomme@arm.com>
+
+	* config/arm/arm-cpus.in (cortex-m33): Add nodsp option.
+	* doc/invoke.texi: Document +nodsp as a valid extension for
+	-mcpu=cortex-m33.
+
 2017-10-16  Martin Liska  <mliska@suse.cz>
 
 	* sbitmap.c (bitmap_bit_in_range_p_checking): New function.

gcc/config/arm/arm-cpus.in

@@ -1532,6 +1532,7 @@ begin cpu cortex-m33
  architecture armv8-m.main+dsp
  fpu fpv5-sp-d16
  option nofp remove ALL_FP
+ option nodsp remove armv7em
  costs v7m
 end cpu cortex-m33
 

gcc/doc/invoke.texi

@@ -15813,6 +15813,9 @@ Permissible names for this option are the same as those for
 The following extension options are common to the listed CPUs:
 
 @table @samp
+@item +nodsp
+Disable the DSP instructions on @samp{cortex-m33}.
+
 @item  +nofp
 Disables the floating-point instructions on @samp{arm9e},
 @samp{arm946e-s}, @samp{arm966e-s}, @samp{arm968e-s}, @samp{arm10e},