board: add SDHCI support for PIC32MZDASK board.

Enable MMC, SDHCI, FAT_FS support for PIC32MZ[DA] StarterKit.
Also add custom scripts, rules to boot Linux from microSD card.

Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
diff --git a/configs/pic32mzdask_defconfig b/configs/pic32mzdask_defconfig
index 1c968fc..55ba3f8 100644
--- a/configs/pic32mzdask_defconfig
+++ b/configs/pic32mzdask_defconfig
@@ -9,7 +9,6 @@
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="dask # "
 # CONFIG_CMD_IMLS is not set
-# CONFIG_CMD_EXPORTENV is not set
 # CONFIG_CMD_SAVEENV is not set
 CONFIG_LOOPW=y
 CONFIG_CMD_MEMTEST=y
@@ -22,6 +21,8 @@
 CONFIG_CMD_TIME=y
 CONFIG_OF_EMBED=y
 CONFIG_CLK=y
+CONFIG_DM_MMC=y
+CONFIG_PIC32_SDHCI=y
 CONFIG_PINCTRL=y
 # CONFIG_PINCTRL_FULL is not set
 CONFIG_SYS_VSNPRINTF=y