x86: fsp: Enlarge the size of malloc() pool before relocation

After fsp_init() returns, the stack has already been switched to a
place within system memory as defined by CONFIG_FSP_TEMP_RAM_ADDR.
Enlarge the size of malloc() pool before relocation since we have
plenty of memory now.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>