ga_IE and en_IE locales: Revert first_weekday removal (bug 24200).

These values were removed by the commit 0a410e76.

	[BZ #24200]
	* localedata/locales/ga_IE (first_weekday): Add, set to 2 (Monday).
	* localedata/locales/en_IE (first_weekday): Likewise.