tpm_tis_spi: Add compatible string atmel,attpm20p

Commit 4f2a348 ("arm64: dts: imx8mm-venice-gw73xx: add TPM device")
added a devicetree node for the Trusted Platform Module on certain
Gateworks boards.

The commit only used the generic "tcg,tpm_tis-spi" compatible string,
but public documentation shows that the chip is an ATTPM20P from Atmel
(nowadays Microchip):
https://trac.gateworks.com/wiki/tpm

Add the chip to the supported compatible strings of the TPM TIS SPI
driver.

For reference, a datasheet is available at:
https://ww1.microchip.com/downloads/en/DeviceDoc/ATTPM20P-Trusted-Platform-Module-TPM-2.0-SPI-Interface-Summary-Data-Sheet-DS40002082A.pdf

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@kernel.org>
Cc: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>

drivers/char/tpm/tpm_tis_spi_main.c

@@ -327,6 +327,7 @@ static const struct spi_device_id tpm_tis_spi_id[] = {
 MODULE_DEVICE_TABLE(spi, tpm_tis_spi_id);
 
 static const struct of_device_id of_tis_spi_match[] __maybe_unused = {
+	{ .compatible = "atmel,attpm20p", .data = tpm_tis_spi_probe },
 	{ .compatible = "st,st33htpm-spi", .data = tpm_tis_spi_probe },
 	{ .compatible = "infineon,slb9670", .data = tpm_tis_spi_probe },
 	{ .compatible = "tcg,tpm_tis-spi", .data = tpm_tis_spi_probe },