spi: dt-bindings: amlogic, meson-gx-spicc: Fix schema for meson-g12a

spi@13000: clock-names: Additional items are not allowed ('pclk' was unexpected)
spi@13000: clock-names: ['core', 'pclk'] is too long
spi@13000: clocks: [[2, 23], [2, 258]] is too long
spi@15000: clock-names: Additional items are not allowed ('pclk' was unexpected)
spi@15000: clock-names: ['core', 'pclk'] is too long
spi@15000: clocks: [[2, 29], [2, 261]] is too long

Conditional schema properties don't overwrite others. Instead of
restrictions have to be validated. So general clock amount is 1-2 and
depending on the actual device type limit the mount to 1 or 2.

Signed-off-by: Alexander Stein <alexander.stein@mailbox.org>
Link: https://lore.kernel.org/r/20200609165527.55183-1-alexander.stein@mailbox.org
Signed-off-by: Mark Brown <broonie@kernel.org>