fix: initialize boot assets with defaults early

The problem was that bootloaders were correctly picking up defaults for
`installer` mode (vs. `imager` mode), but DTB and other SBC stuff wasn't
properly initialized, so installing on SBC fails.

Now all options are properly initialized with defaults early in the
process.

Fixes #8009

Signed-off-by: Andrey Smirnov <andrey.smirnov@siderolabs.com>

cmd/installer/pkg/install/install.go

@@ -151,6 +151,8 @@ func NewInstaller(ctx context.Context, cmdline *procfs.Cmdline, mode Mode, opts
 		}
 	}
 
+	i.options.BootAssets.FillDefaults(opts.Arch)
+
 	bootLoaderPresent := i.bootloader != nil
 	if !bootLoaderPresent {
 		if mode.IsImage() {

internal/app/machined/pkg/runtime/v1alpha1/bootloader/grub/install.go

@@ -31,8 +31,6 @@ func (c *Config) Install(options options.InstallOptions) error {
 		return err
 	}
 
-	options.BootAssets.FillDefaults(options.Arch)
-
 	if err := utils.CopyFiles(
 		options.Printf,
 		utils.SourceDestination(

internal/app/machined/pkg/runtime/v1alpha1/bootloader/sdboot/sdboot.go

@@ -165,8 +165,6 @@ func (c *Config) Install(options options.InstallOptions) error {
 		}
 	}
 
-	options.BootAssets.FillDefaults(options.Arch)
-
 	if err := utils.CopyFiles(
 		options.Printf,
 		utils.SourceDestination(