fbdev: fbmem: allow overriding the number of bootup logos

Probably most useful if you want no logo at all, or if you only want one
logo regardless of how many CPU cores you have.

Signed-off-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190827110854.12574-3-peda@axentia.se
diff --git a/Documentation/fb/fbcon.rst b/Documentation/fb/fbcon.rst
index 65ba402..e57a3d1 100644
--- a/Documentation/fb/fbcon.rst
+++ b/Documentation/fb/fbcon.rst
@@ -174,6 +174,11 @@
 	displayed due to multiple CPUs, the collected line of logos is moved
 	as a whole.
 
+9. fbcon=logo-count:<n>
+
+	The value 'n' overrides the number of bootup logos. 0 disables the
+	logo, and -1 gives the default which is the number of online CPUs.
+
 C. Attaching, Detaching and Unloading
 
 Before going on to how to attach, detach and unload the framebuffer console, an