arm: config: enforce -fno-pic for gcc

Android's tool chain enable the -mandroid at default.
This option will enable the -fpic, which cause uboot compilation
failure:
"
 LD      u-boot
 u-boot contains unexpected relocations: R_ARM_ABS32
 R_ARM_RELATIVE
"

In my testcase, arm-linux-androideabi-gcc-4.9 internally
enables '-fpic', so when compiling code, there will be
relocation entries using type R_ARM_GOT_BREL and .got
section. When linking all the built-in.o using ld, there
will be R_ARM_ABS32 relocation entry and .got section
in the final u-boot elf image. This can not be handled
by u-boot, since u-boot only expects R_ARM_RELATIVE
relocation entry.
arm-poky-linux-gnueabi-gcc-4.9 default does not enable '-fpic',
so there is not .got section and R_ARM_GOT_BREL in built-in.o.
And in the final u-boot elf image, all relocation entries are
R_ARM_RELATIVE.

we can pass '-fno-pic' to xxx-gcc to disable pic. whether
the toolchain internally enables or disables pic, '-fno-pic'
can work well.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Reviewed-by: Tom Rini <trini@konsulko.com>