pcu_l1_if_phy: add new PHY API function to disconnect PDCH

There is a function l1if_connect_pdch, but no complementary function
like we have it with l1if_open_pdch and l1if_close_pdch. The reason for
this is that the PHY implementations that rely on a femtocell DSP do not
need to disconnect the pdch explcitly. However, the planned support for
the E1 based Ercisson RBS CCU will require an explicit disconnect. So
lets add a function call for this.

Change-Id: Ied88f3289bda87c48f5f9255c4591470633cc805
Related: OS#5198
diff --git a/src/pcu_l1_if_phy.h b/src/pcu_l1_if_phy.h
index 73d0b6f..318d0aa 100644
--- a/src/pcu_l1_if_phy.h
+++ b/src/pcu_l1_if_phy.h
@@ -7,4 +7,5 @@
 int l1if_connect_pdch(void *obj, uint8_t ts);
 int l1if_pdch_req(void *obj, uint8_t ts, int is_ptcch, uint32_t fn, uint16_t arfcn, uint8_t block_nr, uint8_t *data,
 		  uint8_t len);
+int l1if_disconnect_pdch(void *obj, uint8_t ts);
 int l1if_close_pdch(void *obj);