arm: am437x: cm-t43: Enable DM for MMC, USB, SPI, SPI_FLASH, enable BLK

Enable driver model for USB, MMC, SPI and SPI_FLASH. Also enable BLK.
This will remove the following compile warnings:

===================== WARNING ======================
This board does not use CONFIG_DM_MMC. Please update
the board to use CONFIG_DM_MMC before the v2019.04 release.
====================================================
===================== WARNING ======================
This board does not use CONFIG_DM_USB. Please update
the board to use CONFIG_DM_USB before the v2019.07 release.
====================================================
===================== WARNING ======================
This board does not use CONFIG_DM_SPI_FLASH. Please update
the board to use CONFIG_SPI_FLASH before the v2019.07 release.
====================================================
Target was compile tested, build was clean.

Signed-off-by: Suniel Mahesh <sunil.m@techveda.org>