msm: ipa3: add a dispatcher layer for IPA APIs

The dispatcher layer enables compilation of IPA 2.x and IPA 3.0
drivers, which shares the same external API, at the same time. The
dispatcher implements all of the external APIs. This implementation
calls a function pointer which is populated by each sub driver.

For example: ipa_connect() is implemented in ipa_api.c. According to the
DTS file, ipa2_connect() will be called for IPA 2.x driver, and
ipa3_connect() will be called for IPA 3.0 driver.

Change-Id: I34ca837094c8c0940f0e267fbc94746414d64d8f
Acked-by: Ady Abraham <adya@qti.qualcomm.com>
Signed-off-by: Nadine Toledano <nadinet@codeaurora.org>
Signed-off-by: Amir Levy <alevy@codeaurora.org>
Signed-off-by: Gidon Studinski <gidons@codeaurora.org>