omap: spl: fix build break due to changes in FAT

omap: spl: fix build break due to changes in FAT

FAT library now uses malloc() and free(). But SPL doesn't
have heap until now. Setup a heap in SDRAM to fix this issue.

However this increases SPL footprint beyond the available SRAM
budget. So, compile out some fancy features in the SDARM init
bring back footprint under control

CC: Sandeep Paulraj <s-paulraj@ti.com>
CC: Wolfgang Denk <wd@denx.de>
Signed-off-by: Aneesh V <aneesh@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>