pixman: disable iwmmxt

pixman: disable iwmmxt

Pixman build system is borked and always wants iwmmxt intrinsics
it errors like below

| ../pixman/.libs/libpixman-1.so: error: undefined reference to
'__builtin_arm_wand'
| ../pixman/.libs/libpixman-1.so: error: undefined reference to
'__builtin_arm_wsrlhi'
| ../pixman/.libs/libpixman-1.so: error: undefined reference to
'__builtin_arm_walign'

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>