drivers/pci/controller: Remove "select SRCU"

Now that the SRCU Kconfig option is unconditionally selected, there is
no longer any point in selecting it.  Therefore, remove the "select SRCU"
Kconfig statements.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
Cc: Rob Herring <robh@kernel.org>
Cc: "Krzysztof Wilczyński" <kw@linux.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: <linux-pci@vger.kernel.org>
Acked-by: Lorenzo Pieralisi <lpieralisi@kernel.org>
Reviewed-by: John Ogness <john.ogness@linutronix.de>