arm: partial revert of r11-8168 [PR100067]

This is a partial revert of r11-8168.  The overall purpose of the
commit is retained (to fix a bogus warning when -mfpu=<not-auto> is
used in combination with eg -mcpu=neoverse-v1), but it removes the
hunk that changed the subsequent feature bits for features of a
simd/fp unit that cannot be described by -mfpu.  While I still think
that is the correct direction of travel, it's somewhat disruptive and
not appropriate for late stage4.  I'll revisit for gcc-12.

gcc:
	PR target/100067
	* config/arm/arm.c (arm_configure_build_target): Do not strip
	extended FPU/SIMD feature bits from the target ISA when -mfpu
	is specified (partial revert of r11-8168).