alsa-utils: fix build for x86 on x86-64

alsa-utils included two ugly patches for ARM and AVR32 to fix build
issues encountered with ncurses. In fact these build issues were
caused by the fact that alsa-utils was using ncurses5-config of the
host instead of the one installed in $(STAGING_DIR).

Therefore, these two patches are removed, and we instead pass
ac_cv_prog_ncurses5_config to the ./configure script.

This commit solves bug #569, reported by Simon Pasch, who also
contributed this fix.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>