make: Specify source files to include

Replace use of wildcard with list of source files to include. The `-y`
suffix is added, but has no significance since conditional compilation
has not been added yet.

Signed-off-by: Tim Crawford <tcrawford@system76.com>

src/ec/ite/ec.mk

@@ -1,5 +1,14 @@
 # SPDX-License-Identifier: GPL-3.0-only
 
+ec-y += ec.c
+ec-y += espi.c
+ec-y += gpio.c
+ec-y += i2c.c
+ec-y += kbc.c
+ec-y += pmc.c
+ec-y += ps2.c
+ec-y += signature.c
+
 ifeq ($(EC_VARIANT), it8587e)
 # SRAM is 4096 bytes, but SRAM at address 2048 is used for scratch ROM
 SRAM_SIZE=2048