Remove the X attribute from .mk files

Bug: 111538404
Test: presubmit
Change-Id: Iefd39e76559ec25c4bdd98893dfc593816da5077
Signed-off-by: Roman Kiryanov <rkir@google.com>
diff --git a/target/board/generic_x86_64/BoardConfig.mk b/target/board/generic_x86_64/BoardConfig.mk
old mode 100755
new mode 100644
diff --git a/target/board/generic_x86_64_arm64/BoardConfig.mk b/target/board/generic_x86_64_arm64/BoardConfig.mk
old mode 100755
new mode 100644
diff --git a/target/board/generic_x86_64_arm64/device.mk b/target/board/generic_x86_64_arm64/device.mk
old mode 100755
new mode 100644