[musl][bootloader] Use compiler-provided standard headers

<stdalign.h>, <stdarg.h>, <stdbool.h>, <stddef.h>, <stdint.h>
are all provided by the compiler and should not be replaced here.

The bootloader code's local versions were sloppy in what names
got defined where, so the code needed some #include additions
and type adjustments.

TC-32 #done

Change-Id: Ib24ba7b5072e99ec9302a6994d63ad5e16233151

[kernel][libc] printf(): Remove unused code for %f (floating point numbers)

Remove the code for handling %f and %a from the two copies of the
printf() implementation in the codebase:

* The kernel's copy (kernel/lib/libc/printf.c). In this case, the
"%f"-handling code was not being compiled -- it was conditional on
"#if !WITH_NO_FP", but kernel code was compiled with WITH_NO_FP set
to 1. We can also remove some related test code.

Note that using the double and float types is generally not allowed
in kernel code anyway (see docs/kernel_invariants.md).

* The bootloader's copy (bootloader/lib/printf.c). This was being
compiled in, but was not being used. (I checked that the
bootloader still works with this removed.)

Change-Id: Id3e7730ef66ce9d6e5f2f95e77625f33d8ddcb05

[bootloader] Initial import of gigaboot

Original source:
https://fuchsia.googlesource.com/gigaboot20x6/
Upstream commit:
80eef665f1e248eafe48f9b430fdae702ece20c1

Change-Id: I1be9ad20831e0d790937446febc28755943884a5