configs: dra7xx-evm: increase the size of the malloc's pool before relocation

This is required to take advantage of MULTI_DTB_FIT before relocation.
If it is too low, DM will be initialized only after relocation has
taken place. That is too late for the DRA7 because I2C DM is used before
the relocation to setup the voltages required, among other things, to
properly initialize the DRAM.
Signed-off-by: NJean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: NTom Rini <trini@konsulko.com>
Reviewed-by: NHeiko Schocher <hs@denx.de>

configs/dra7xx_evm_defconfig

 CONFIG_ARM=y
 CONFIG_ARCH_OMAP2PLUS=y
 CONFIG_TI_COMMON_CMD_OPTIONS=y
-CONFIG_SYS_MALLOC_F_LEN=0x2000
+CONFIG_SYS_MALLOC_F_LEN=0x18000
 CONFIG_OMAP54XX=y
 CONFIG_TARGET_DRA7XX_EVM=y
 CONFIG_SPL=y