ARM: uniphier: increase CONFIG_SYS_MALLOC_F_LEN to bind all nodes

In the next commit, I will add "u-boot,dm-pre-reloc" to the "soc"
(simple-bus) nodes in UniPhier device trees.  But, before that,
CONFIG_SYS_MALLOC_F_LEN must be increased.

Adding "u-boot,dm-pre-reloc" to a simple-bus node causes it to bind
all of its child nodes.  (See simple_bus_post_bind() function)

Actually, I want only UART0 and pinctrl to be bound in SPL and before
relocation in U-boot proper.  But, with "u-boot,dm-pre-reloc" in the
simple-bus node, all the other unwanted nodes are also bound.  The
default value for CONFIG_SYS_MALLOC_F_LEN, 0x400, is not enough for
that.  Increase the pre-reloc malloc size to 0x2000, hoping the root
cause will be fixed later.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>