[Silabs] silabs fix buildscript

[jepenven-silabs]

Add activate step prior to gn generation when not using SLC

[github-actions]

PR #25898: Size comparison from ae17dc1 to 7f8e4a2

Increases (1 build for nrfconnect)

platform	target	config	section	ae17dc1	7f8e4a2	change	% change
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	text	805144	805148	4	0.0

Full report (6 builds for cc32xx, nrfconnect, qpg)

platform	target	config	section	ae17dc1	7f8e4a2	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	645769	645769	0	0.0
			(read/write)	203848	203848	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197248	197248	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	933102	933102	0	0.0
			.debug_aranges	87704	87704	0	0.0
			.debug_frame	301596	301596	0	0.0
			.debug_info	20310043	20310043	0	0.0
			.debug_line	2681003	2681003	0	0.0
			.debug_loc	2827360	2827360	0	0.0
			.debug_ranges	286352	286352	0	0.0
			.debug_str	3041144	3041144	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105953	105953	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	380543	380543	0	0.0
			.symtab	257472	257472	0	0.0
			.text	537696	537696	0	0.0
nrfconnect	all-clusters-app	nrf52840dk_nrf52840	(read only)	4	4	0	0.0
			(read/write)	1174112	1174112	0	0.0
			bss	155557	155557	0	0.0
			rodata	132640	132640	0	0.0
			text	805144	805148	4	0.0
	all-clusters-minimal-app	nrf52840dk_nrf52840	(read only)	4	4	0	0.0
			(read/write)	1119168	1119168	0	0.0
			bss	154713	154713	0	0.0
			rodata	109456	109456	0	0.0
			text	774356	774356	0	0.0
	all-clusters-app	nrf7002dk_nrf5340_cpuapp	(read only)	4	4	0	0.0
			(read/write)	1434132	1434132	0	0.0
			bss	135297	135297	0	0.0
			rodata	228692	228692	0	0.0
			text	776068	776068	0	0.0
qpg	lighting-app	qpg6105+debug	(read/write)	1152952	1152952	0	0.0
			.bss	96036	96036	0	0.0
			.data	852	852	0	0.0
			.text	600048	600048	0	0.0
	lock-app	qpg6105+debug	(read/write)	1121528	1121528	0	0.0
			.bss	91172	91172	0	0.0
			.data	856	856	0	0.0
			.text	568628	568628	0	0.0