Update mpg123 to 1.25.2
Change download URL to Sourceforge
Change deprecated checksum variable (PKG_MD5SUM) to PKG_HASH
Add libout123
Add generic optimizations depending on platform have fpu or not
Add NEON-specific optimization
Remove BUILD_PATENTED, reference:
https://github.com/openwrt/packages/pull/4587
Small cleanup of Makefile
Thanks to Ted Hess for reviewing and suggesting compilation fix

NOTE:
mpg123 uses the most recent approach just like ffmpeg that's
mentioned here: https://github.com/openwrt/packages/pull/4555

Signed-off-by: Daniel Engberg <daniel.engberg.lists@pyret.net>