Remove some warnings when using checkpatch with --strict option

Some checks are ignored as they do not match TF-A coding rules:
PREFER_KERNEL_TYPES, USLEEP_RANGE
or MISRA:
COMPARISON_TO_NULL, UNNECESSARY_PARENTHESES

Change-Id: I335ede89fc872a6169028552d1ba9312fc61a0ba
Signed-off-by: Yann Gautier <yann.gautier@st.com>

.checkpatch.conf

@@ -73,3 +73,19 @@
 # BRACES reports this kind of messages:
 # braces {} are not necessary for any arm of this statement
 --ignore BRACES
+
+# PREFER_KERNEL_TYPES reports this kind of messages (when using --strict):
+# "Prefer kernel type 'u32' over 'uint32_t'"
+--ignore PREFER_KERNEL_TYPES
+
+# USLEEP_RANGE reports this kind of messages (when using --strict):
+# "usleep_range is preferred over udelay; see Documentation/timers/timers-howto.txt"
+--ignore USLEEP_RANGE
+
+# COMPARISON_TO_NULL reports this kind of messages (when using --strict):
+# Comparison to NULL could be written ""
+--ignore COMPARISON_TO_NULL
+
+# UNNECESSARY_PARENTHESES reports this kind of messages (when using --strict):
+# Unnecessary parentheses around ""
+--ignore UNNECESSARY_PARENTHESES