Rename config.h to mbedtls_config.h

This commit was generated using the following script:

# ========================
#!/bin/sh
git ls-files | grep -v '^ChangeLog' | xargs sed -b -E -i '
s/((check|crypto|full|mbedtls|query)_config)\.h/\1\nh/g
s/config\.h/mbedtls_config.h/g
y/\n/./
'
mv include/mbedtls/config.h include/mbedtls/mbedtls_config.h
# ========================

Signed-off-by: Bence Szépkúti <bence.szepkuti@arm.com>
diff --git a/docs/3.0-migration-guide.d/remove-null-entropy.md b/docs/3.0-migration-guide.d/remove-null-entropy.md
index 50e024a..c38c930 100644
--- a/docs/3.0-migration-guide.d/remove-null-entropy.md
+++ b/docs/3.0-migration-guide.d/remove-null-entropy.md
@@ -1,7 +1,7 @@
 Remove the option to build the library without any entropy sources
 ------------------------------------------------------------------
 
-This does not affect users who use the default `config.h`, as this option was
+This does not affect users who use the default `mbedtls_config.h`, as this option was
 already off by default.
 
 If you were using the `MBEDTLS_TEST_NULL_ENTROPY` option and your platform