soc/tegra: pmc: Use BIT macro for register field definition

Use BIT macro for register field definition and make constant as U
when using in shift operator like (3 << 30) to (3U << 30)

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>