soc/intel_adsp: Remove spurious 4k padding of .text section

There was a ". = ALIGN(4096);" sitting at the end of the .text section
in the linker.  This had the effect of needlessly padding the size of
the segment as packed into and copied out of the firmware DMA image.

There's no value to storing unused bytes in the image.  It also makes
analysis easier for changes the modify code size.  The following
.rodata section was already being 4k aligned anyway.

Signed-off-by: Andy Ross <andrew.j.ross@intel.com>