PCI: tegra194: Create debugfs directory only when CONFIG_PCIEASPM is enabled

Previously, the debugfs directory was unconditionally created in
tegra_pcie_config_rp() regardless of the CONFIG_PCIEASPM setting.
This led to unnecessary directory creation when ASPM support was disabled
since only ASPM state count was exposed through debugfs.

Hence, move the debugfs directory creation into init_debugfs() which is
conditionally compiled based on CONFIG_PCIEASPM. This ensures that both
the directory and 'aspm_state_cnt' entry are only created when ASPM is
enabled and avoids cluttering debugfs with empty directories when ASPM is
disabled.

Signed-off-by: Hans Zhang <18255117159@163.com>
[mani: subject and description change]
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/20250407124331.69459-1-18255117159@163.com