Revise -mdisable-fpregs option and add new -msoft-mult option

The behavior of the -mdisable-fpregs is confusing in that it doesn't
disable the use of the floating-point registers in all situations.
The -msoft-float disables the use of the floating-point registers in
all situations.  The Linux kernel only needs to disable use of the
xmpyu instruction to avoid using the floating-point registers.

This change revises the -mdisable-fpregs option to disable the use of
the floating-point registers in all situations.  It is now equivalent
to the -msoft-float option.  A new -msoft-mult option is added to
disable use of the xmpyu instruction.  The libgcc library can be
compiled with the -msoft-mult option to avoid using hardware integer
multiplication.

2021-10-24  John David Anglin  <danglin@gcc.gnu.org>

gcc/ChangeLog:

	* config/pa/pa-d.c (pa_d_handle_target_float_abi): Don't check
	TARGET_DISABLE_FPREGS.
	* config/pa/pa.c (fix_range): Use MASK_SOFT_FLOAT instead of
	MASK_DISABLE_FPREGS.
	(hppa_rtx_costs): Don't check TARGET_DISABLE_FPREGS.  Adjust
	cost of hardware integer multiplication.
	(pa_conditional_register_usage): Don't check TARGET_DISABLE_FPREGS.
	* config/pa/pa.h (INT14_OK_STRICT): Likewise.
	* config/pa/pa.md: Don't check TARGET_DISABLE_FPREGS. Check
	TARGET_SOFT_FLOAT in patterns that use xmpyu instruction.
	* config/pa/pa.opt (mdisable-fpregs): Change target mask to
	SOFT_FLOAT.  Revise comment.
	(msoft-float): New option.

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