mmc: zynq_sdhci: Add xilinx_pm_request weak function

mmc: zynq_sdhci: Add xilinx_pm_request weak function

Mini emmc does not use any pmufw and ZYNQMP_FIRMWARE is disabled.
xilinx_pm_request() will not be compiled and causes undefined reference to
`xilinx_pm_request' error. So add a weak function in zynq_sdhci.c file.

Signed-off-by: T Karthik Reddy <t.karthik.reddy@xilinx.com>
Signed-off-by: Ashok Reddy Soma <ashok.reddy.soma@xilinx.com>
Link: https://lore.kernel.org/r/1633086518-32636-1-git-send-email-t.karthik.reddy@xilinx.com
Signed-off-by: Michal Simek <michal.simek@xilinx.com>