sandbox: Move CONFIG_TPM_TIS_SANDBOX to Kconfig

Move this over to Kconfig and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/sandbox_defconfig b/configs/sandbox_defconfig
index dd33028..c8c888d 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -22,3 +22,4 @@
 CONFIG_SYS_I2C_SANDBOX=y
 CONFIG_SANDBOX_SPI=y
 CONFIG_SPI_FLASH_SANDBOX=y
+CONFIG_TPM_TIS_SANDBOX=y