qcacld-3.0: Add kbuild cpp flag for low power mode feature

Add cpp flag support for CONFIG_ENABLE_LOW_POWER_MODE in Kbuild.
Currently, this config is enabled for wearables only.

Change-Id: I2fb08930290f5c23641e1d76796ab829b31aae04
CRs-Fixed: 3110291

Kbuild

@@ -2964,6 +2964,7 @@ WLAN_TWT_SAP_STA_COUNT ?= 32
 ccflags-y += -DWLAN_TWT_SAP_STA_COUNT=$(WLAN_TWT_SAP_STA_COUNT)
 endif
 
+cppflags-$(CONFIG_ENABLE_LOW_POWER_MODE) += -DCONFIG_ENABLE_LOW_POWER_MODE
 cppflags-$(CONFIG_WLAN_TWT_SAP_PDEV_COUNT) += -DWLAN_TWT_AP_PDEV_COUNT_NUM_PHY
 cppflags-$(CONFIG_WLAN_DISABLE_EXPORT_SYMBOL) += -DWLAN_DISABLE_EXPORT_SYMBOL
 cppflags-$(CONFIG_WIFI_POS_CONVERGED) += -DWIFI_POS_CONVERGED