target/hppa: fix TLB handling for page 0

target/hppa: fix TLB handling for page 0

Assume the following sequence:

pitlbe r0(sr0,r0)
iitlba r4,(sr0,r0)
ldil L%3000000,r5
iitlbp r5,(sr0,r0)

This will purge the whole TLB and add an entry for page 0. However
the current TLB implementation in helper_iitlba() will store to
the last empty TLB entry, while helper_iitlbp() will write to the
first empty entry. That is because an empty entry will match address
0 in helper_iitlba()

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Message-Id: <20190311191602.25796-3-svens@stackframe.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>