gd: bump to version 2.1.0

Drop obsolete/applied patches. Refresh the rest, and add sequence numbers.

Add a patch fixing build against uClibc when UCLIBC_HAS_LONG_DOUBLE_MATH is
missing.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>