ARM: imx: mxs: Add support for imx287 based BTT devices

ARM: imx: mxs: Add support for imx287 based BTT devices

The btt[c3] devices are based on imx287 SoC.

U-Boot SPL 2025.04-01081-g07e086681d26 (Apr 16 2025 - 12:24:36 +0200)
Trying to boot from MMC1

U-Boot 2025.04-01081-g07e086681d26 (Apr 16 2025 - 12:24:36 +0200)

CPU:   Freescale i.MX28 rev1.2 at 454 MHz
BOOT:  SSP SPI #3, master, 3V3 NOR
Model: BTT3
Board: LWE BTT SoM HW rev 0
DRAM:  256 MiB
Core:  86 devices, 15 uclasses, devicetree: separate
MMC:   MXS MMC: 0
Loading Environment from SPIFlash... SF: Detected is25lp128 with page
                    size 256 Bytes, erase size 64 KiB, total 16 MiB
OK
In:    serial@80074000
Out:   serial@80074000
Err:   serial@80074000
Net:   eth0: ethernet@800f0000
Hit any key to stop autoboot:  0

Signed-off-by: Lukasz Majewski <lukma@denx.de>