PCI: dwc: Replace bit rotation operation (1 << bit) with BIT(bit)

Replace bit rotation operation (1 << bit) with BIT(bit), which
simplifies code reading.

No functional change is intended.

Signed-off-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Joao Pinto <jpinto@synopsys.com>
Cc: Jingoo Han <jingoohan1@gmail.com>