This introduces some new environment variable helpers and updates
the existing ones. Newly introduced are:
getenv_bool: read a bool variable
getenv_ul: read an unsigned long variable
getenev_uint: read an unsigned int variable
getenv_nonempty: like normal getenv, but does return NULL instead of an
empty string
All new helpers take a pointer to the value. This value is only modified
when the variable exists. This allows the following programming scheme:
unsigned int myvalue = sanedefault;
getenv_uint("myvalue", &myvalue);
So without checking the return value myvalue contains the best possible
value.
getenv_ull is updated to this scheme.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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