mhi: controller: Do not enable/disable L1 from device side

Enable/disable L1 from device side requires to access PCIe
registers over the link which could be in L1SS sleep. This
can delay read until device comes out of retention. If read
happens with spin lock held it can starve other tasks for
long duration. Fix this issue by removing lpm_enable/lpm_disable
call back.

Change-Id: I5cc3a9008ab4e7cc344d403bb3c14b1d6e156b6c
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>