meta-audio-4a-framework: bump recipes to latest revs

meta-audio-4a-framework: bump recipes to latest revs

4a-hal-generic now bumped to RC2

Use ${AGL_APP_REVISION} for all gerrit repos:
 * 4a-alsa-core/4a-alsa-core_git.bb:SRCREV = "${AGL_APP_REVISION}"
 * 4a-hal-unicens/4a-hal-unicens_git.bb:SRCREV = "${AGL_APP_REVISION}"
 * agl-service-audio-4a/agl-service-audio-4a_git.bb:SRCREV = "${AGL_APP_REVISION}"

Use SHA1 for external (github) repos:
 * 4a-hal-generic/4a-hal-generic_git.bb:SRCREV = "25ec9ead44e7429b673a60d347a55d0086578e75"
 * 4a-softmixer/4a-softmixer_git.bb:SRCREV = "e173f942334e741714ac45924554552b5511de1d"

Change-Id: Ic1215f9b0a786e9496ea448483c3a4b78be37c7e
Signed-off-by: Stephane Desneux <stephane.desneux@iot.bzh>