Allow override own number as voicemail number for GSM

KEY_CONFIG_TELEPHONY_USE_OWN_NUMBER_FOR_VOICEMAIL_BOOL only take effect
for CDMA.
Also let it be able to take effect for GSM condition

Bug: b/120452825
Test: Build pass and Field testing pass for Sprint SIM
Change-Id: I012f5d358d6e95de543d021bc81dc23361581aea