qoriq: new target

qoriq: new target

Add a new target named "qoriq", that will support boards using PowerPC
processors from NXP's QorIQ brand.

This doesn't actually add support for any board yet, so that
installation instructions can go in the commit message of the commit
that adds actual support for a board.

Using CONFIG_E6500_CPU here due to the kernel using -mcpu=powerpc64
rather than -mcpu=e5500 when selecting CONFIG_E5500_CPU. The only
difference between e5500 and e6500 is AltiVec support, and the kernel
checks for it at runtime. Musl will only check at runtime if AltiVec
support is disabled at compile-time, so we need to use e5500 in CPU_TYPE
to avoid SIGILL.

Math emulation (CONFIG_MATH_EMULATION_HW_UNIMPLEMENTED) is required, as
neither e5500 nor e6500 implement fsqrt nor fsqrts, and musl hardcodes
sqrt and sqrtf to use these ASM instructions on PowerPC64.

Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Reviewed-by: Rui Salvaterra <rsalvaterra@gmail.com>