mediatek: add support for BananaPi BPi-R4 Lite

mediatek: add support for BananaPi BPi-R4 Lite

The BPi-R4 Lite is a WiFi-7 router board based on the MT7987 SoC.

Specification :
 - SOC: Mediatek MT7987A (4x Cortex-A53
 - RAM: 2GB
 - Flash: 32MB SPI NOR, 256MB SPI NAND, 8GB eMMC
 - Switch: MediaTek MT7531AE
 - Ports : 4x LAN (1G), 1x SFP (via MT7531), 1x WAN (2.5G)
 - Buttons : Reset & WPS/Mesh
 - LEDs : Status (PWM), SFP
 - USB: on-board VIA VL817 USB3.1/USB2.0 hub
    * 1 - mPCIe B (SIM3)
    * 2 - NGFF-KEYB (SIM1)
    * 3 - USB-A connector
    * 4 - mPCIe A (SIM4)
 - mPCIe: 1x 8GT/s x2 or 2x 8GT/s x1 (configurable via bootloader)
 - RTC: PCF8563
 - mikroBUS socket with SPI, I2C and full UART
 - on-board HT42B534 USB-to-serial for Type-C console port
 - Power: USB Type-C PD 20V, or DC via barrel connector or JST-VH 3.96

Installation:
Uncompress *sdcard.img.gz and write to microSD card, eg. using 'dd'.
Use bootloader menu on the serial console to install SPI-NAND or SPI-NOR,
once installed to SPI-NAND you can use the bootloader menu to install to
eMMC. See instructions for BananaPi R3 for details.

Signed-off-by: Daniel Golle <[email protected]>