firmware: imx: Add stub functions for SCMI MISC API

To ensure successful builds when CONFIG_IMX_SCMI_MISC_DRV is not enabled,
this patch adds static inline stub implementations for the following
functions:

  - scmi_imx_misc_ctrl_get()
  - scmi_imx_misc_ctrl_set()

These stubs return -EOPNOTSUPP to indicate that the functionality is not
supported in the current configuration. This avoids potential build or
link errors in code that conditionally calls these functions based on
feature availability.

This patch also drops the changes in commit 540c8302 ("firmware: imx:
remove duplicate scmi_imx_misc_ctrl_get()").

The original change aimed to simplify the handling of optional features by
removing conditional stubs. However, the use of conditional stubs is
necessary when CONFIG_IMX_SCMI_MISC_DRV is n, while consumer driver is
set to y.

This is not a matter of preserving legacy patterns, but rather to ensure
that there is no link error whether for module or built-in.

Fixes: 0b4f8a68 ("firmware: imx: Add i.MX95 MISC driver")
Reviewed-by: Cristian Marussi <cristian.marussi@arm.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>