include: gas: sframe: fix terminology from offset to data word

include: gas: sframe: fix terminology from offset to data word

In SFrame V3, with the addition of flexible FDE type, the
variable-length array of bytes trailing the SFrame FRE header are no
longer exclusively interpreted as signed offsets. This data can now
include unsigned control data, unsigned padding word data or signed
offset data. Consequently, using the term "offsets" to describe this
trailing data is inaccurate and can be confusing.

This patch switches the terminology to 'Data Word' across the assembler
and the SFrame header file. Note that, the term 'Word' is used
colloquially here, the actual size (1, 2, or 4 bytes) remains determined
by the applicable bits in the FRE info byte.

gas/
	* gen-sframe.c: Rename SFrame FRE 'offset' to 'data word'.
include/
	* sframe.h (SFRAME_FRE_DATAWORD_1B, SFRAME_FRE_DATAWORD_2B,
	SFRAME_FRE_DATAWORD_4B): New constants.
	(struct sframe_fre_info): Update bitfield documentation.
	(SFRAME_V3_FRE_DATAWORD_COUNT): New macro.
	(SFRAME_V3_FRE_DATAWORD_SIZE): New macro.