Fix LE Audio toggle missing issue for dual mode hearing device

After the code change of ag/28283226, they hide the LE Audio toggle for
LE Audio only device since turning off the profile may cause this device
no functioning. But the dual mode hearing devices(LE Audio + Asha) are
wrongly recognized as LE Audio only devices since
HearingAidProfile.accessProfileEnabled() return false. This make the
users lost the ability to switch between profiles they preferred.

Make HearingAidProfile.accessProfileEnabled() return true and hide the
Hearing Aid toggle by default since it's also meaningless to turn off
the Asha profile for Asha-only devices.

Flag: com.android.settingslib.flags.asha_profile_access_profile_enabled_true
Bug: 356530795
Test: manual checking the UI
Change-Id: I7e20416fccbefad484cf9e5106248984e61216c2