docs: admin-guide: hw_random: Make document title more generic and concise

The hw_random subsystem no longer works only on specific Intel chipsets;
make the title of hw_random.rst reflect this fact.

While we're at it, also remove the words "Linux support for", since it's
clear from context that this is a document about Linux.
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Link: https://lore.kernel.org/r/20221101160119.955997-1-j.neuschaefer@gmx.netSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/hw_random.rst

-==========================================================
-Linux support for random number generator in i8xx chipsets
-==========================================================
+=================================
+Hardware random number generators
+=================================
 
 Introduction
 ============