Convert CONFIG_SYS_CACHE_STASHING to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_CACHE_STASHING

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/T2080QDS_NAND_defconfig b/configs/T2080QDS_NAND_defconfig
index 0a83ed1..f947561 100644
--- a/configs/T2080QDS_NAND_defconfig
+++ b/configs/T2080QDS_NAND_defconfig
@@ -14,6 +14,7 @@
 CONFIG_ENABLE_36BIT_PHYS=y
 CONFIG_SYS_BOOK3E_HV=y
 CONFIG_SYS_FSL_CPC=y
+CONFIG_SYS_CACHE_STASHING=y
 CONFIG_SYS_MPC85XX_NO_RESETVEC=y
 CONFIG_SPL_SYS_MPC85XX_NO_RESETVEC=y
 CONFIG_PCIE1=y