cypress-firmware: update it to version 5.4.18-2021_0812

cypress-firmware: update it to version 5.4.18-2021_0812

- Binary files were renamed to cyfmac from brcmfmac, but the files needs
  to be on the router with the previous naming

[    6.656165] brcmfmac: brcmf_fw_alloc_request: using brcm/brcmfmac43455-sdio for chip BCM4345/6
[    6.665182] brcmfmac mmc1:0001:1: Direct firmware load for brcm/brcmfmac43455-sdio.bin failed with error -2
[    6.674928] brcmfmac mmc1:0001:1: Falling back to sysfs fallback for: brcm/brcmfmac43455-sdio.bin

- Cypress were acquired by Infineon Technologies
Thus change the project URL and switch to download files from their
GitHub repository. This is much better than the previous solution, which
requires finding new threads on their community forum about new driver
updates, and it will be necessary to change the URL each time.

Unfortunately, it seems that there is not published changelog, but
according to this forum thread [1], be careful by opening the link from
solution since it contains ending bracket ), it brings fixes for various
security vulnerabilities, which were fixed in 7_45_234.

Fixes:
- FragAttacks
- Kr00k

Also add LICENSE file

Run tested on Seeedstudio router powered by Raspberry Pi 4 CM with
package cypress-firmware-43455-sdio.

Before:
root@OpenWrt:~# dmesg | grep 'Firmware: BCM4345/6'
[    6.895050] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Mar 23 2020 02:20:01 version 7.45.206 (r725000 CY) FWID 01-febaba43

After:
root@OpenWrt:~# dmesg | grep 'Firmware: BCM4345/6'
[    6.829805] brcmfmac: brcmf_c_preinit_dcmds: Firmware: BCM4345/6 wl0: Apr 15 2021 03:03:20 version 7.45.234 (4ca95bb CY) FWID 01-996384e2

[1] https://community.infineon.com/t5/Wi-Fi-Bluetooth-for-Linux/Outdated-brcmfmac-firmware-for-Raspberry-Pi-4-in-OpenWrt-21-02-1/m-p/331593#M2269

Signed-off-by: Josef Schlehofer <pepe.schlehofer@gmail.com>