soc/intel/cmn/usb: Add helper macro for USB 3.0 port TX configuration

Introduce the `USB3_PORT_TX_CFG` macro to simplify the definition of
`usb3_port_config` structures.

This macro allows platform code to easily configure the Transmit
De-emphasis (`tx_de_emp`) value for a specific USB 3.0 port (identified
by `ocpin`).

This improves readability and reduces boilerplate when tuning signal
integrity settings for different USB ports on the board.

TEST=Able to build and boot google/kinmen.

Change-Id: I42565e2c573dfcff244a81bf7bcb9749eca52c05
Signed-off-by: Subrata Banik <subratabanik@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90021
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>

src/soc/intel/common/block/include/intelblocks/usb.h

@@ -137,6 +137,13 @@ struct usb3_port_config {
 	.tx_downscale_amp = 0x00, \
 }
 
+#define USB3_PORT_TX_CFG(pin, de_emp) { \
+	.enable           = 1, \
+	.ocpin            = (pin), \
+	.tx_de_emp        = (de_emp), \
+	.tx_downscale_amp = 0x00, \
+}
+
 struct tcss_port_config {
 	uint8_t enable;
 	uint8_t ocpin;