package/pkg-utils: prevent KCONFIG_ENABLE_OPT from changing =m to =y

The KCONFIG_ENABLE_OPT is intended to enable a required kernel configuration
option when a package requires it.

However, this will often override an existing enabled module with `=m` with `=y`
which overrides the module to be built-in instead of separate.

This is undesirable behavior; we often want these as `=m` and not `=y` to reduce
the size of the kernel image.

This patch changes KCONFIG_MUNGE_DOT_CONFIG to prevent changing `=m` to `=y`.

Signed-off-by: Christian Stewart <christian@paral.in>
Co-authored-by: TIAN Yuanhao <tianyuanhao3@163.com>
Cc: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
[yann.morin.1998@free.fr:
  - drop  || exit 1, it is superfluous
  - don't change the match in the SED (just append &&)
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/pkg-utils.mk

@@ -22,12 +22,17 @@ KCONFIG_DOT_CONFIG = $(strip \
 
 # KCONFIG_MUNGE_DOT_CONFIG (option, newline [, file])
 define KCONFIG_MUNGE_DOT_CONFIG
-	$(SED) "/\\<$(strip $(1))\\>/d" $(call KCONFIG_DOT_CONFIG,$(3))
+	$(SED) "/\\<$(strip $(1))\\>/d" $(call KCONFIG_DOT_CONFIG,$(3)) && \
 	echo '$(strip $(2))' >> $(call KCONFIG_DOT_CONFIG,$(3))
 endef
 
 # KCONFIG_ENABLE_OPT (option [, file])
-KCONFIG_ENABLE_OPT  = $(call KCONFIG_MUNGE_DOT_CONFIG, $(1), $(1)=y, $(2))
+# If the option is already set to =m or =y, ignore.
+define KCONFIG_ENABLE_OPT
+	$(Q)if ! grep -q '^$(strip $(1))=[my]' $(call KCONFIG_DOT_CONFIG,$(2)); then \
+		$(call KCONFIG_MUNGE_DOT_CONFIG, $(1), $(1)=y, $(2)); \
+	fi
+endef
 # KCONFIG_SET_OPT (option, value [, file])
 KCONFIG_SET_OPT     = $(call KCONFIG_MUNGE_DOT_CONFIG, $(1), $(1)=$(2), $(3))
 # KCONFIG_DISABLE_OPT  (option [, file])