x86/msr: Add rdmsrl_on_cpu() compatibility wrapper

Add a simple rdmsrl_on_cpu() compatibility wrapper for
rdmsrq_on_cpu(), to make life in -next easier, where
the PM tree recently grew more uses of the old API.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Mario Limonciello <mario.limonciello@amd.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Xin Li <xin@zytor.com>
Link: https://lore.kernel.org/r/20250512145517.6e0666e3@canb.auug.org.au